Tsuna finally managed to collect himself. He took a deep breath and did his best to ignore literal Satan sitting on his bed. He had not even known the Chaos Gacha had a Familiar category.
Her being a familiar implied he had some level of control over her. That, and her calling him Master. Still, he did not fully trust it. Demons were known to slip out of contracts, and this was quite literally the King of Hell. Forgive his distrust.
[Congratulations on getting your first familiar! The Chaos Gacha is filled with countless treasures, and loyal servants just happen to be one of them. Do not worry about controlling your newfound familiar. Everything from a common dog to eldritch abominations that defy reason are completely loyal to you. They might say things to mess with you, but they will always stand on your side, even against their own nature. If you are still nervous, you can send your familiar back to the familiar space whenever you wish. They can only function in your reality as long as you allow it.]
The information flooded his mind. Tsuna studied the Duke of Hell, who waved at him while giggling. Her stunning looks and the fact that she could not betray him were not able to hold back the tense feeling in his chest.
He drew in a steady breath and chose to speak.
Lucifer beat him to it.
"Finally. I was starting to lose hope you would talk to me, Master. So what is it going to be? A stern warning? Barring me from your presence for eternity? Or perhaps you will order me to lop off my head and present it to you?" she said lightly, completely unconcerned.
She knew he did not trust her. She was practically offering test scenarios.
Tsuna sighed, some of the tension leaving his shoulders.
"It would be easier to banish you to the Familiar space. Forget about the literal ruler of Hell sitting here looking infuriatingly adorable. But that would be hell. Sending you into eternal isolation just for what you are." He rubbed his temple and offered an awkward smile. "I do not trust you. You know that. But I am not cruel enough to do that."
Her smile sharpened with amusement.
"Oh my. My Master is such a softie. I appreciate the opportunity you have given me. It is wise not to trust a demon, even if it wounds me that my Master thinks so little of little ole me. Perhaps my infuriatingly adorable looks will win your trust and affection eventually." She batted her eyes innocently.
"Affection? I seem to recall one of your abilities is to enslave souls with a kiss," Tsuna said flatly. He could tell she was messing with him, and it did take some of the tension off his shoulders.
Lucifer chuckled and leaned back against the bed.
"It is. But I would never use it on you, Master. Swear to God and hope to die and all that," She said nonchalantly with a bright grin.
"Are you any good at tutoring?" Tsuna asked after a moment. She was a demon, but from the description in her bio, she was a highly capable one.
Lucifer blinked, then laughed.
"Quite literally the best you will find, Master. There is nothing in this world I cannot master. I am Big G's greatest creation, after all." She tossed her hair smugly.
"So you can teach me about Dying Will Flames?" Tsuna asked lightly, already making plans to train with her.
Reborn was excellent, but she was the Devil. Her knowledge should surpass his.
Hearing his question, she twitched, and the light, confident smile on her face cracked. She looked like she had taken a physical blow.
"No. That is not a field I am experienced in," she spoke between gritted teeth, as if saying those words was carving up her throat.
Then she leaned forward, nearly nose to nose.
"But give me time, Master, and I will master it. I will bring you knowledge not even gods possess." she spoke quickly, her eyes bright and that same manic energy boiling off her.
Tsuna laughed lightly. She flinched again.
"So your knowledge is not quite as all knowing as you implied." Tsuna said after a moment. Again she flinched, then let out a huff and looked at him with a pout.
"Fine. I am not Big G. I cannot know everything. But I learn fast enough that it hardly matters. The problem is that my world does not have Dying Will Flames. This is my first exposure to them. I have seen chi, and there are parallels, but I need more time to study before I can explain properly."
Tsuna frowned briefly. Her world? That implied she was not part of this one. He knew the Chaos Gacha was powerful, but it might be reaching far beyond what he thought possible.
Interesting.
"All right. The flames can wait. But you can help with normal subjects like math and science, right?" Tsuna asked lightly.
Lucifer nodded vigorously.
"Simple as pie. I could make you a Nobel Prize winner in a year. And I have other uses. That toddler set up surveillance throughout your home. I looped everything the moment I entered this dimension. Your secrets are safe, Master." She puffed her chest proudly.
Tsuna cursed under his breath about Reborn but let it go. He did not have many secrets worth hiding.
Except Lucifer.
"Thank you, Luci. I hope this partnership lasts. I am sending you back for now. I need to check on Nagi." Tsuna spoke out with a small smile.
Lucifer pouted but nodded.
"If you must. But if you need help with the girl, I am available. I can teach tricks that would make succubi blush, and I am quite skilled with humans. I could have her family leave her in your care easily." Lucifer said, waiting for Tsuna to banish her for now.
Tsuna rolled his eyes at the first part but paused at the second.
"You could have Nagi staying here? Just to be clear, I do not want you to mind-control the couple or kill them," Tsuna said after a moment
Lucifer clicked her tongue.
"What am I, an amateur? Only losers mind-whammy mortals. It is not a sin if they don't choose the path themselves. I will simply make them too busy to care for her by nudging their greed. From what you know, they are already halfway there. Give me a couple of days and she will be under your mother's care. If you allow me to act, I can guarantee she stays tonight." Lucifer promised with a smug smile.
Tsuna hesitated, then relented.
"Okay, get to it. But I want you to report everything you are doing on the hour," Tsuna relented.
Lucifer rolled her eyes but nodded.
"As you wish, Master. Now go spend time with your little girlfriend. I have work to do." She spoke out, opening the window and jumping out with effortless grace.
Once she was gone, Tsuna exhaled slowly, unease settling in his chest.
He had just unleashed the Devil onto his world and was trusting the Chaos Gacha and her word to hold the leash.
He was probably a terrible person.