Vegapunk held the failed devil fruit in his hand as he said, "Are you sure about this? You won't be able to undue this and it could weaken your sword."
"Weaken it, how?"
Vegapunk held up the fruit as he pointed towards the two other fruits and said, "If its power isn't stable, it would always be a weaker version of one of those."
Marcus shrugged as he said, "That's the one my sword wants and they're my partner in serious battles, so I'm fine letting them pick the fruit they want. Besides, it's not like a defective devil fruit will make us weaker. Physical strength, haki and swordsmanship are my main strengths and that won't change."
Vegapunk took one last glance at the fruit before he said, "I understand, it's your choice to make in the end."
Vegapunk waved Marcus towards a sealed chamber as he said, "Let's go in there and get your sword set up."
Marcus followed Vegapunk into the chamber before he helped set up his sword in a weird contraption. It held his sword slightly drawn from its sheath with the blade resting right above the defective devil fruit. Connected to the contraption were a bunch of thick metal pipes that went up and disappeared into the ceiling.
Vegapunk checked everything over before he pulled out a small vial of red liquid. As Vegapunk uncorked the vial, Marcus said, "What's that stuff? It almost looks like blood."
"It's very similar to blood and it's also what allows this process to work. It acts as the catalyst for the devil fruit to bond with an inanimate object." Vegapunk said and he carefully applied the liquid to Eternal Rest.
"That being said, I've never tried it on an item like yours… This step might not be necessary for this to work, but better safe than sorry."
Marcus watched with wide eyes as the liquid didn't drip from the blade and almost seemed like a paste even though it looked like a liquid when inside the vial. As Vegapunk finished getting everything ready Marcus asked, "Does that thing have a shelf life?"
"Not that I've found. This batch was made about two years ago and still works fine."
Marcus glanced at where Vegapunk put the vial in his pocket before he asked, "Is that easy to make?"
"Vegapunk finished getting everything set up before he asked, "With the right lab equipment… Why do you want some?"
"Not right now, but I wouldn't mind some at a later date… Although I'd rather have a fresh batch when the time comes."
Vegapunk gestured for Marcus to move out of the room as he said, "You want to use it on something else?"
"Yeah, at least I'll give it a try… I'll still need to find a proper devil fruit for the whole thing. But they do say fortune favors the bold."
Vegapunk sealed the large door to the room before he moved over to a control panel as he said, "Is that a saying? I haven't heard that one before but I like it."
Vegapunk's hands moved over the panel as some lights powered up on the panel and a couple monitors nearby started displaying data. Marcus watched the whole process before he asked, "Is all this necessary? Doesn't my sword just need to cut into the fruit?"
"This is to monitor everything and record the data properly. That's the main reason I agreed to do this."
Marcus nodded slightly as Vegapunk finished a few more things before he grabbed a lever and turned to look at Marcus as he said, "Fortune favors the bold, huh? I think trusting your sword for picking a defective is rather bold…"
Vegapunk pulled the lever down and a moment later the thing his sword was mounted on slowly descended. It only took seconds but as Marcus held his breath while he watched, everything seemed to slow as he focused on his sword. Time seemed to stop for him as his sword touched the defective devil fruit. The blade moved at a snail's pace in his eyes as it sliced into the fruit.
Vegapunk's hands looked like a blur to Marcus as they moved across the control panel. But his focus was completely on his sword as Vegapunk said something that sounded muffled and distant to Marcus. As the blade sliced a quarter inch into the fruit, Marcus saw what looked like a hint of flames ghost across the exposed blade. A moment later Marcus's entire sword and sheath exploded in yellowish orange flames before it disappeared from view as the room was engulfed in fire.
Marcus's eyes widened as he turned towards Vegapunk only to find the man excitedly talking as his hands moved over the control panel. Only Marcus couldn't hear a word the man said because of the blood pounding in his ears. Marcus took deep breaths to calm his heart that was trying to explode from his chest before he asked, "What was that? I couldn't hear you."
"I said the data from this is incredible. The heat is higher than I expected, unfortunately it just destroyed the sensors so I have no clue if it's more powerful than the original."
Marcus frowned slightly as he asked, "Wouldn't destroying the sensors mean it's more powerful than the original?"
"Unfortunately no, it doesn't. I don't currently have sensors that can withstand that type of heat. So I have no way to test it properly."
Marcus stared through the glass at the room full of fire before he asked, "Now what? Do we need to wait or can I go get my sword?"
Vegapunk glanced at the room full of fire himself before he said, "Maybe you should wait for the fire to stop before you go inside…"
"No, I refuse to believe my sword will hurt me."
Vegapunk glanced at the sealed room again and let out a sigh before he said, "Alright, I'll unlock the door for you…"
Vegapunk hit something on his control panel and Marcus heard the door slowly unlock. Vegapunk actually moved away from the door as Marcus moved closer before he grabbed the large wheel on it. Marcus spun the wheel which released the final barrier keeping the door sealed before he pushed it open. Flames erupted from the door like a massive blow torch, but Marcus felt nothing from them. When he stepped into the room though, he felt the heat from everything else in the room.
Marcus started to sweat as his shoes melted on the super heated metal floor before he coated his shoes in haki to stop it. Afterwards Marcus walked towards the center of the room through the flames that blocked his vision. It took a minute as Marcus couldn't really see properly, but he reached the thing his sword was on and grabbed his sword's hilt.
The moment his hand wrapped around his sword, two things happened. The heat he felt from everything else in the room seemed to disappear before the flames pulled back and condensed into the woman who saved him from Doflamingo's last attack. They both looked at each other for a few moments as heat waves wafted off of everything around them before Marcus asked in a shaky voice, "Are… Are you my mother?"
The woman made of flames sadly shook her head before she reached out and gently caressed Marcus's face before he asked, "Then you're the spirit of the sword itself?"
The woman nodded as she smiled at Marcus while she continued to caress his cheek before he asked, "I wanna thank you for saving me… But I also wanna know, why did you do it?"
The flaming woman moved her mouth to speak, but when nothing came out she frowned and tilted her head slightly. After a few moments she pointed to his hand holding the sword hilt before she pointed at him and then herself before she raised up a single finger. Marcus frowned slightly trying to figure out what she meant before he asked, "Do you consider us to be one?"
The woman nodded with a smile on her face again before Marcus said in a confused tone, "But couldn't you just find a new user if I died? You were my mothers and grandfather's sword before I ever picked you up…"
The woman shook her head and pointed to his chest before she pointed at her own which caused Marcus to frown again. The woman stared at him for a few moments before one of her finger tips started to shoot out fire. She used that finger to write out, 'family' on the metal pedestal the defective devil fruit used to be on. Marcus looked at the word for a few moments before he asked in a confused tone, "You… You only want to be wielded by someone who is part of my family?"
The woman nodded before she pulled him into a hug and kissed his cheek before she disappeared into the sword itself. Marcus stood there stunned for a few moments as he rubbed his cheek before he mumbled, "What is it with girls kissing me for no reason…"
Marcus removed his sword from the slightly melted pillar before he unsheathed it completely to look at it. Marcus instantly noticed the change in the blade, it now looked older, almost rusted in color and he felt a tiny pull on his stamina just holding it right now. After studying it for a few minutes, Marcus sheathed it and the drain on his stamina instantly disappeared. Slightly confused he drew the sword partly and he felt the stamina drain again until he sheathed it.
Marcus tested it a few more times before he placed his sword on his waist and walked out to be greeted by Vegapunk who excitedly asked, "That was fascinating… When can we study the capabilities of your sword?"
"Either make a larger, fire proof room or set up an area outside where I can test it properly."
Vegapunk nodded as he said, "Give me a few days and we can test it outside."
Vegapunk glanced at the Mera Mera no Mi and the other failed devil fruit before he asked, "What about the other failed clone? Do you want that along with the original?"
"If you don't mind, I'll gladly take it."
Vegapunk waved it off as he said, "That's fine, it didn't cost much to make and you're also letting me study your sword."
After talking a little longer with Vegapunk, Marcus collected the two fruits into a small chest before he called Kuma. On the call he checked in with him and asked if he could come pick up the two fruits and to give them to his brothers. Sabo was to get the cloned fruit while Ace would get the original. After that call, Marcus headed outside to test his sword out and get used to it.
Marcus found a spot close to the laboratory and away from the forest to test out his sword. It was a rocky area next to the mountains with almost no vegetation, so Marcus didn't need to worry about causing a massive fire. Before Marcus tested his sword's new power he first tested how it affected his stamina. He could feel the tiniest pull when the sword was unsheathed but it was so small it honestly wouldn't affect him. If anything he was already thinking of ways he could use it for training.
Once Marcus finished his normal sword training he attempted to have the sword use its devil fruit powers. But it was incredibly awkward because the sword couldn't read his mind so he had to tell it what he wanted it to do. Needless to say, Marcus quickly realized he would need to come up with move names and say them out loud to use them. Something he kind of already did, but it was normally a whisper to himself instead of actually speaking or yelling them out.
As for the stamina drain when using the devil fruit, it wasn't as bad as he thought it would be. Sure for large scale attacks it took more then Marcus would like. But for normal attacks and concentrated flames on his sword, the drain was almost nothing. In the end, all it really meant was Marcus needed to train more and focus on his stamina training.