One day, Tsunade-sama waited for her in a large clearing.
"I want to introduce you to someone today," she said with a smile. "She has been with me for many years, and I know she will serve you faithfully as well. Kuchiyose no jutsu."
From the enormous cloud of smoke, a giant white and blue slug appeared. Yes, a slug. Seina stared at it while the slug, which seemed to be the chief summoning slug, lowered itself and curved its eyes to look at her.
"Hello again, Tsunade-sama," said the enormous slug in a very feminine voice.
"Katsuyu, I wanted to introduce you to my apprentice," Tsunade nodded. "This is Seina. I'd like her to sign your contract."
"Oh? A new apprentice? That's fine."
A large scroll appeared at her feet. Tsunade-sama opened it, revealing the countless names that had served alongside Katsuyu over the years. The last name was that of the Hokage.
"I know you have some type of summoning with your powers," Tsunade said, sitting beside her, "but Katsuyu is a medical summoning. With her help, you'll be able to heal many people at once, especially considering your enormous chakra reserves. Honestly, Seina, you'd make much better use of Katsuyu than I ever could. It's time she had a new summoner."
"Do you have that much chakra, Seina-san?" asked Katsuyu with curiosity.
"Call me Seina," she requested. "I'm the jinchuriki of the Kyubi and an Uzumaki."
"Wow. I've never had a summoner with your characteristics. It will be an honor to serve by your side."
"Alright. I'll sign the contract," she smiled. "Should I write my real name or the name everyone knows?"
"It doesn't really matter. What matters is your blood."
She cut her finger with a kunai and wrote her name in blood next to Tsunade Senju's. Since practically no one would see what was written, she used her real name.
"Seina Namikaze? You're the Fourth Hokage's daughter!" the slug exclaimed. "I didn't expect that."
"Alright! Katsuyu, please return. Seina will try to summon you right after."
Katsuyu disappeared, nodding. Tsunade-sama didn't even explain what to do, so she molded her chakra, in the same amount she had seen the Hokage use, and summoned Katsuyu. Or at least she tried.
"Wait. I want to try something," Kurama requested. "Mold your chakra along with mine and summon her."
"What are you-"
She restarted, using both her chakra and the chakra Kurama offered her, and summoned Katsuyu. The enormous slug appeared again, glowing almost imperceptibly with a demonic orange chakra. She even seemed to vibrate with the abnormal energy given to her.
"Incredible!" Katsuyu shouted, instead of speaking softly as before. "This must be…"
"The Kyubi's chakra?" Tsunade-sama asked, wide-eyed. "You molded your chakra with the bijuu's to summon her!"
"Kurama asked me to," she shrugged. "Now I see why."
"I feel as if I have triple the energy, Tsunade-sama, Seina-sama."
"You don't need to use honorifics with me."
"You are my summoner, the daughter of the late Hokage, and the apprentice of the new Hokage," Katsuyu replied succinctly.
"Wait!" the Hokage interrupted. "Katsuyu, how many people do you think you could heal with the energy you have now without Seina transferring more chakra?"
"Easily 400 or 500 people."
The Hokage turned to her with an astonished expression. Seina smiled. When Tsunade-sama realized what had just happened, her lips stretched into a somewhat malicious smile.
"Did you know that this form of Katsuyu is just an incomplete form?" Tsunade-sama informed her. "The slugs of the Shikkotsu Forest are actually all the same entity. Together, they form the true form of Katsuyu."
"Does that mean you're much larger, Katsuyu?" she asked the slug in amazement.
"Yes. The portion of chakra Tsunade-sama uses to summon me in this size is designed to leave her room to fight and heal at the same time. You used the same amount of chakra as her, so my size is the same as when Tsunade-sama summoned me."
"What would happen if I summoned you with much more chakra? What proportion of your real size are you now?"
"This form represents only 5% of me."
Seina almost choked on her tongue upon realizing that the true form of Katsuyu was colossal. She couldn't imagine it. The slug in front of her was as large as the Hokage's mansion, somewhat larger than the chief toad Naruto had summoned. She turned breathlessly to the Hokage, who was already waiting for her gaze.
"I want to try it," she declared like a lunatic.
She dispelled all the clones she had studying to gather all her chakra in herself. The Hokage nodded with the face of someone about to start playing with her favorite toy. Katsuyu disappeared without saying anything.
"Kurama-"
"I know. Let's go. This is finally getting interesting!" the bijuu exclaimed inside her.
Considering the chakra she had spent to form only 5% of Katsuyu, she made the relevant calculations and divided the cost in half. One half she would provide with her own chakra, the other half she would receive from Kurama. Even so, she had more than enough.
"Kuchiyose no jutsu!"
The chakra expenditure was much greater, but much less than expected considering Kurama's help. The slug that appeared… She couldn't see its face. She lifted her head, her neck hurting, but couldn't see the end until Katsuyu bent back down to the ground.
"It's the first time I've set foot in the outside world in my entirety…" Katsuyu said in awe. Her voice, despite being very feminine, was deep due to her gigantic size.
"I can't believe it," Tsunade-sama whispered beside her. "I've only seen Katsuyu this size in her natural habitat, once."
"Eh… maybe we didn't think this through," Seina cut in, pointing to part of the forest that had been buried under the summoning.
Fortunately, part of her body was summoned in the river and the large clearing they had been in.
"How big must she be?"
"460 meters."
"Damn…" Tsunade-sama said, her voice catching. "It's going to take a while to get to the top."
"Tsunade-sama!" several voices shouted.
Seina saw with some horror, and growing laughter, the shocked faces of the ninjas who had come to her training site upon seeing the giant slug. She didn't know some of them, but others, like Genma, looked at the summoning with open mouths as if they couldn't believe it.
"Oh, guys. I was just practicing with my apprentice the summoning of Katsuyu."
"Is this Katsuyu!?" one asked fearfully.
"The complete form, yes."
"Sorry for the inconvenience, minna-san," Katsuyu spoke, bending down even further to look below.
"No need to apologize," Tsunade-sama waved her hand. "What we need to do is keep practicing. Ah, and figure out how to get to your head without taking 5 minutes. You can return to your posts!"
Seina watched as some retreated reluctantly, curious about what was happening there. She waited until everyone had left before turning to the summoning.
"I think I have the solution. Katsuyu, do you mind if I put something with one of my seals on top of your head? That way I could use the hiraishin and appear there."
"That's fine."
"Great! Kuchiyose no jutsu."
She used the summoning jutsu again to call one of her winged creations. Tsunade-sama and Katsuyu watched attentively, the Hokage with bright eyes, as her white abraxan with its enormous wings appeared.
"Let's fly up," she said to Tsunade-sama, jumping onto the patiently waiting animal.
"I can't believe I'm riding a winged horse created from nothing…" the Hokage murmured behind her.
The flight was relatively short. While flying, she tried to compare Katsuyu's height to some monument she had visited. The first that came to mind was the Eiffel Tower, but according to Fleur's information, it was only 330 meters tall. Katsuyu far exceeded that height. She jumped from the abraxan onto Katsuyu's head. It was so large that her house and all its land could fit, with space to spare.
"What a view," Tsunade-sama smiled.
She noticed the Hokage's attentive gaze as she pulled an ordinary stone from her pouch, enchanted it to be indestructible, used a sealing jutsu on it, and attached it to that spot on Katsuyu's head with a permanent spell.
"Does this bother you?" she asked the slug.
"Not at all. I don't even notice it."
"Great! Now I can get up here in less than a millisecond!"
Tsunade-sama couldn't suppress a laugh. She spent the afternoon with Katsuyu by her side to get used to the chakra expenditure needed to keep her there. Even with the chief slug present, the chakra expenditure was a drop in the ocean with Kurama's help. They also practiced acid attacks, splitting into smaller slugs, and quickly recombining.
"My biggest disadvantage is my speed," Katsuyu said at the end of the training. "Compared to Manda or Gamabunta, I am the slowest summon."
"Hmm... Can I try something?" Seina asked.
"What do you plan to do?"
"Make her lighter," she replied. "I can do it easily with my powers."
"And how long will this jutsu last?"
"Until I remove it, obviously. Actually, it's an advantage having Katsuyu's complete form here, because when I activate this jutsu, each part of her will be less heavy."
"Which will give her greater speed due to her new lightness."
"Can you lighten my weight, Seina-sama? It would be a great advantage for me."
She used the spell on Katsuyu's gigantic form, noticing a rapid exhaustion of her magic. While it was true that she wouldn't need to renew the spell unless she deactivated it with a finite, that didn't mean it required little magic to cast it for the first time. Her magic, unlike her chakra, did not have Kurama's almost limitless reserves. She thanked the power at her disposal or she would have fainted on the spot.
Tsunade-sama grabbed her arm when she staggered, making her sit on the ground. She saw her master's green hand touch her forehead, but knew she wouldn't be able to perceive what was happening to her.
"Too much expenditure at once. I'll be fine. I just need to eat."
"I imagine you have some food in your fantastic pouch. Eat. We're done for today," she turned to look at the summon. "How do you feel, Katsuyu?"
"Very light, Tsunade-sama."
They watched as she decomposed, faster than before, and her smaller parts seemed to slide quickly across the ground as if skating on ice.
"Quite impressive," muttered the Hokage with a smile. "We will have to practice, you and I too, Katsuyu. You can go rest now."
"Understood, Tsunade-sama. Until next time!"
"Come on. Now it's time to eat and recover. Tomorrow will be another day."
As she walked back to her house through the village, she noticed many more looks than she was used to. Most, if not all, were from ninjas who had seen Katsuyu and already gossiped that it had been her who managed to summon her. She ignored them, pretending they weren't there, and kept walking. It was expected that she would gain some reputation among the ninja forces. If not for her work at the hospital, then for being the Hokage's apprentice. As long as it didn't negatively affect her or her team, she didn't care.
When she got home, she saw that she was alone. She read the note left by Naruto and Sasuke, who were on a joint mission, and ate while reading a book. She knew that Kakashi-sensei would take days to return to the village from his mission, so she had no qualms about having dinner and locking herself in her bathroom to relax her muscles.
"It hasn't been bad this afternoon," Kurama said suddenly. She jumped in the water. "You've already seen what we can do with hardly any effort. I'm looking forward to the old hag giving you the green light to train with the plant guy."
"With Tenzou?"
"Yeah, that one."
"We'll have to train far from the village. You saw what happened today."
"Meh. You can't hide who you are. They'll have to deal with it and accept it."
"I suppose..."
A couple of days later, even though nothing had really changed, she noticed how some ninjas began to bow their heads when she passed by. Mostly chunins, some jonin, and the hospital ninjas. She didn't know why they were making such a fuss now. Maybe because they hadn't paid enough attention to her progress before. Summoning Katsuyu's complete form, something even the Hokage couldn't do, apparently deserved respect. To her, it only showed that she had more chakra, but people were easily impressed, so she stopped thinking about it.
She was walking through the village, looking for the bookstore, when she saw Kakashi-sensei in the distance heading towards the Hokage tower. She wondered if she should greet him, but supposed he was very busy. Still, she saw Genma stop him under the shade of a tree. If she hadn't been observing and had her spell active, she wouldn't have seen the exchange.
"Kakashi, I finally find you. What the hell have you been teaching your kunoichi?"
"Hello, Kakashi. How are you? How was your mission?" Kakashi-sensei said sarcastically. "Let's see, what has Seina done now?"
She listened as Genma aborted a laugh at the jonin's expectant, and unsurprised, question.
"I don't know! Maybe summoning Katsuyu's complete form, or creating and using a new genjutsu on Hayate that knocked him out, or perhaps giving you a bracelet that- you know. She used the Kyubi's chakra to summon Katsuyu, Kakashi. She hasn't even been out of the academy for a year! Who would think of such a thing?"
"She did, obviously," her master replied boredly. "You don't know even a quarter of what she does and thinks about daily, Genma. Besides, why are you telling me all this?"
"I was one of her father's bodyguards, Kakashi," Genma whispered to him. "I've been watching from afar, as best I could, and now-"
"And now she reminds you of her father? Tell me about it. Naruto is a spitting image of Kushin-"
"Not just that! She's surpassing her father, by far," he said worriedly. "Minato had an entry in the bingo book of other countries. How long do you think it will take for Seina to have her own photograph in that book?"
"All we can do is train her, just as Tsunade-sama, Tenzou, Yugao, Hayate, Guy, and I are doing. Still, it amuses me that you think she can't take care of herself. Although it may not seem like it, she could run circles around most ninjas in Konoha."
"I've been talking with Raido. Do you think Seina would accept if we trained her too?"
"Yes. She loves learning new things, so she won't turn you down."
"Great. Let's see if I can find her to talk to her."
Seina suppressed a smile. She silenced herself and appeared on the branch above their heads. Kakashi-sensei looked up the moment her feet touched the tree.
"Look. Here she is," he said to Genma. "Didn't you want to talk to her?"
"Where did you come from!?"
"Wait for me," Kakashi-sensei requested, ignoring the other jonin. "I won't take long."
Seina sat on the branch, watching him enter the Hokage Tower. Genma jumped up next to her, squatting down.
"Did you hear all that? How did you do it? I didn't notice you."
Seina pointed to her earring, though she didn't use it to eavesdrop like her team did. Her earring functioned as a poison detector.
"The bracelet isn't the only thing I can make. I heard you."
"You- Ugh. I see. I'll assume you heard everything. So?"
"Like Kakashi-sensei said, I enjoy learning new things. You're an expert in poisons, right?"
"Among other things, yes. Raido and I are both taijutsu specialists. Raido has a lot of experience as an assassin and is an expert in kenjutsu. If you train with Yugao and Hayate, I imagine that interests you."
"True. Honestly, it would be better if you all coordinated amongst yourselves. I have one afternoon off every other day." She shrugged. "I don't have more free time."
"I'll talk to the others," Genma nodded thoughtfully.
They talked about what he planned to teach her, and by extension, her team, when they trained. They also discussed the infamous bingo book where her father had once been listed with an S-rank and an explicit note to "flee immediately." She stifled a sound of disbelief. Her father... the father who had held and cradled her, protected her with his life on the day she was born... had been so dangerous that the bingo book recommended fleeing rather than fighting him with caution.
"Yo. I'm back. I see you two have come to an agreement," Kakashi-sensei said.
She jumped down from the tree, followed by Genma. They bid farewell there, watching the ninja disappear, then headed home.
"...So, you summoned Katsuyu's final form. Why am I not surprised?"
"Hey. Tsunade-sama also wanted to see her," she defended herself. The jonin snorted a laugh. "Besides, it wasn't that big a deal. Half the chakra I used was given to me by Kurama."
"And how big is she?" he asked curiously. "No one has ever seen her complete form."
"According to her, 460 meters."
"...460 meters?" Kakashi-sensei asked, stunned. "Now I understand why Genma was so hysterical. What a way to draw attention. Well, what can you do?"
"I had to place a seal on her to use the hiraishin," she commented, her lip twitching with laughter at the comic situation. "You should have seen Genma's face."
Kakashi-sensei stifled a laugh as he imagined it. When they arrived home, they saw Naruto preparing food.
"Naruto! When did you get back?" she asked, smiling.
"About an hour ago. You were busy at the hospital, so we didn't tell you," Sasuke replied from behind him. "Did you know we ran into Ino and Shikamaru? Apparently, everyone is talking about a certain summoning by a certain person..."
She stifled a laugh at her teammate's pointed look, also avoiding Kakashi-sensei's somewhat exasperated, yet amused expression.
"And we missed it! I want to see her, nee-chan!"
"Maybe outside the village, when she doesn't end up destroying half the forest," she chuckled.
The jonin stifled a groan of exasperation at her declaration while Sasuke shook his head, unsurprised. They ate, talking about what they had done on their mission and what she had learned during their absence. That same afternoon, since Kakashi-sensei had the rest of the day off and it was her free afternoon, they started training in her newly inaugurated training house.
"I still can't believe this place exists, even though I've seen what you did inside the suitcase..."
"But it's great for training! And huuuuge!" Naruto yelled, his voice echoing.
The training house essentially resembled a grand clearing with trees, an enchanted sky, and enormous false windows through which light also entered the side walls. Luckily, the protective runes and spells were enough to keep the structure from being destroyed by the countless jutsus hitting the walls.
"I have something to show you," she told them with a wide, uncontrollable smile.
"You're scaring me," Sasuke admitted.
"Remember when we talked about chakra natures? I've been experimenting with something, and I've managed to create a new ninjutsu by combining two different natures."
It had taken her days to successfully use this unique ninjutsu. She had had to review the theory of hand seals, chakra molding, and even read purely theoretical scrolls from her copied library. Well, her clones did. It had taken over 100 attempts before finding the right combination, but now she understood how to do it.
She conjured a huge rock in the middle of the area. Then she molded her chakra and performed the necessary hand seals. Her jutsu had no name, so she simply shot boiling water and steam from her mouth, which, besides being at a harmful temperature, was also corrosive. Kurama had advised her to use yin chakra as well to corrupt the jutsu, giving it that extra touch. The rock shattered from the force of her water cannon, and seconds later, it began to disintegrate into dust due to the corrosion.
"...Did you just invent a new element?" Sasuke asked.
"No. The boil release is used by some people in Kiri," Kakashi-sensei corrected. "Still... It's incredible."
"I've been testing it, but I need an open space, or it would end up poisoning us all. If I mix Kurama's demonic chakra and then use a spark, it explodes."
"Are you saying you've tried to do that?" the jonin asked seriously.
"Only with a very small amount. The explosion was no bigger than an explosive tag."
"Can we learn to use it?" Naruto asked, jumping with excitement.
"Sure. If Seina explains it to you, it's just a matter of molding the chakra the way she does, with the right amount, and using the proper seals."
Both Sasuke and Naruto turned to her, looking expectant. That's how Naruto and Sasuke started learning the new ninjutsu while Kakashi-sensei and she fought all-out, as always. She ended up exhausted but very satisfied. Despite the progress she had made investigating new jutsus, she knew she would have to ease up or she would burn out, so to speak, before long. She felt like Hermione studying for her fifth-year exams or during her campaign for Minister.
A few days later, Genma and Raido showed up, ready to train. They quickly kept up with her pace, as they were used to training with her father, who had also been an expert in using the hiraishin.
"This reminds me of the old days," Raido exclaimed, wielding his weapon.
"And yet, I'm almost more afraid of his 12-year-old daughter..." Genma muttered under his breath.
"Don't be a whiner, Genma! You know you like it!"
Seina tried out her new jutsu, launching a jet of boiling water and steam. They jumped aside, stifling a scream. Meanwhile, she noticed that it was getting easier and faster for her to mold her chakra and perform the seals. She intercepted them with the hiraishin and a flying kick. Genma crashed into a tree but unfortunately swapped with a log while flying. Still, he couldn't fool her enchanted ears. She reappeared behind him, performing the hand seals for a regular water jutsu. The torrent swept him away. Raido took advantage of her distraction to attack, but a tap on the ground split the rock and destabilized him. Another use of the hiraishin, a feint to dodge his weapon, and with the help of an impedimenta, Seina managed to have enough time to throw him at Genma with a chakra-less punch.
"Ugh. Hold on a moment," said Genma from the ground, soaked from head to toe. "It's not fair that you have so much stamina. We're supposed to be the ones giving you a beating! Not the other way around!"
"What was that last jutsu?" Raido asked, sitting on the grass.
"...How much has Kakashi-sensei told you about my abilities?" she asked, casting a spell to give them privacy.
"Told us about what?"
"That troll hasn't told us anything," Genma replied, drying his clothes with a burst of chakra. "Why?"
"Let's just say I can do a lot of things... Want me to give you an example? Why don't you stand up, seeeenseeei?" she requested, drawing out the syllables with a wicked smile she tried to hide.
"I'm not sure I want to..." Raido nudged him with his elbow. "Alright!"
She cast an invisible tarantallegra. She watched as his feet started dancing uncontrollably in a tap dance, moving him around wildly, jumping and pirouetting, while he shouted and tried to keep his balance with his arms. Raido was speechless, his face a picture, for exactly two seconds. Then he started crying with laughter. That was enough for her to start laughing too, pounding the ground while Genma moved all over the clearing, hopping and tapping his feet rapidly. She ended the spell when she caught her breath.
"I will never forget this moment," Raido swore, wiping tears from his usually serious face.
"What the hell was that!?"
"My example," she grinned widely. "I could have hurt you a lot, considering there's a cliff nearby and I was controlling your feet, don't you think?"
Genma lay on the ground, looking at his legs as if they had betrayed him. Raido and she continued to laugh occasionally, remembering his expression. That's how Kakashi-sensei found them, returning from another mission with his porn book in hand and his face buried in its pages.
"Yo! How did your first training session go?"
"..."
Raido started laughing again, making Kakashi-sensei lift his head and raise an eyebrow at the sound. He only needed to see her mischievous smile to know she had done something.
"Let's just say the lesson was for Genma, but in dancing!" he burst out laughing. He dodged the senbon his friend sent at him. "You missed it."
"Aside from that," his victim sighed with a tired face, "it was a good training session. Seina's kenjutsu style is evident. Now I feel more at ease."
"Yes. We can help her improve, but she already has a good foundation. She just needs practice."