Author's Note: Hello, again! I've gotten questions on Marvin's strength, so I'll answer right now.

Short answer, Marvin is relative to One for All.

Long answer, Marvin is currently equal to a 25% Izuku, possibly 30%. His maximum strength– in his physical body with all his memories– would be greater than Izuku's with a maxed OFA, but he'd be slower than Izuku, so it'd balance out.

His strength in this story is tied to the amount of memories he has. He will also unlock his other ability, the Dominance Factor, as he remembers things. Those who came from Reaper's story should remember it quite well.

For those who don't know, the Dominance Factor is an energy-based Quirk that affects the target's mind. It can technically force the target to experience any emotion but he's only consciously used it for inducing fear in his past life, and thus, hasn't unlocked its full potential.

The Factor can also induce hallucinations, activate or deactivate abilities and tech, paralyze, knock out, and even kill targets. It depends on how much power Marvin puts into it, how much he focuses the Factor, and what he wants.

That may seem too broken, but the Factor does have limits. It can't focus on someone from too far away, it's medium range at most; further than that makes it lose focus and causes collateral damage.

It's heavily dependent on Marvin's mental state, physical health and well-being, and time. If he's weak, tired, or mentally disturbed, his control and power over it diminishes.

It also takes a heavy toll on his body and mental health. Using it even a little against Bakugo in the Battle Trials (which is why Bakugo screamed) enhanced Marvin's nightmare to be severely traumatizing, made him more sensitive to his emotions, and it, combined with the memories, will slowly make him more jaded and closed off.

In total, Marvin's strong, relative to One for All, but has severe limits in place. He will become stronger as the story goes on, just like Izuku, and he'll struggle a lot with his mental health, personality, and trauma like he did in Reaper's story.

I hope that could explain it well; there'll probably be a more in-depth explanation in the story going forward, but this should hopefully cover the basics.

Enjoy the chapter!

.

Izuku barely turned as Momo entered the training room, focusing on learning a kick Marvin was showing him.

It wasn't a surprise now. Momo had readily agreed to help him and arrived around twenty minutes after he did.

Since Izuku had given her access with his card, all Momo had to do when she reached the doors was grab the handle, say her name and the door would open upon recognizing her voice.

"Morning, Izuku," Momo greeted as she set her bag down.

"Hi, Momo!" Izuku grunted as he tried, and failed to perform the kick.

Momo gasped as Izuku landed flat on his back, having overshot and lost his balance.

"Oh god, are you alright?" Momo asked as she approached him.

Izuku groaned and nodded. "Yeah… Just– Just failed the kick."

He put the back of his hands over his eyes as he closed them, trying to catch his breath.

Marvin always ran him ragged, doing combat drills and various exercises that made All Might's training look like a walk in the park.

At least All Might didn't make him force him to sprint across the training room until he crawled.

He was learning though, and each day, Izuku felt a bit more comfortable throwing punches, his kicks a little smoother.

Izuku wasn't anywhere close to a pro, though. Something Marvin had no issues pointing out whenever Izuku lost to the training dummy.

He kipped up, something he'd learned to do only a few days ago, and lifted his shirt, wiping sweat from his brow.

Momo arched an eyebrow to hide the blush. Izuku looked more buff and lean than when Momo met him, still on the thinner side, almost deceiving compared to his strength, but the look suited him.

"Are you ready to train?" Izuku asked, slightly breathless.

"I'm surprised you still are, given the school's closed," Momo replied. "I thought you would've taken the day off."

"I kind of am," Izuku rubbed his neck. "Mostly just practicing movements today. I'm not using my Quirk since Recovery Girl told me to take it easy."

"I'm just–" He yawned and quickly covered his mouth. "I'm just trying to learn some kicks. Nothing much."

"You look exhausted," Momo pointed out in concern. "Have you been sleeping alright?"

"Yeah… Yeah, I'm alright," Izuku gave a half-nod, disliking the need to lie.

He rubbed his eyes tiredly. There'd been another nightmare, a mix of Marvin's and Izuku's, but it was so incoherent that neither could make heads nor tails of it.

In truth, neither of them hadn't gotten good sleep in a while, and the USJ incident had only worsened it.

He saw Nomu's mutilated body whenever he closed his eyes, and the thought always pushed him close to vomiting, so he tried not to dwell on it too much.

Momo's eyes narrowed, and she leaned in suspiciously.

"Are you sure, Izuku?" She asked, ignoring Izuku's wide-eyed blush. "You look almost sick. Should we go see Recovery Girl? That fight yesterday could've affected you."

Izuku pulled at his shirt nervously and gulped. "N–No. I-I'm fine," He told her, avoiding her eyes.

"Izuku, look at me," Momo demanded, moving in front of his eyes.

She stared at him, examining his face, and her features softened.

"Izuku…" She whispered as she checked him. "Izuku, you look exhausted. There are bags under your eyes, and you look so stiff! That isn't normal."

Izuku stepped back, feeling like his face would melt off the bone from the proximity.

"I-I'm fine," He told her, hazily waving it off. "Just… Just a bit tired."

"Then sleep," Momo stated exasperatedly. "You don't have to train today, you know? We don't have classes today."

Izuku shook his head. "I… I can't. I have to train," He said as he groggily took a fighting stance again.

Momo tsked angrily, and a staff shot from her palm.

It whistled through the air towards Izuku's shins, and Marvin suddenly took over.

He leaped over it and kicked off the wall, landing in his starting position with a hand on the ground.

Marvin stood slowly, sighing and rolling his shoulders. "What was the point of that?"

He closed his eyes and cracked his neck as Momo stepped back, eyes wide.

Momo raised her staff in front of her, heart racing.

"Who are you?!" She demanded, gripping her staff tightly.

Marvin cracked open his eyes and raised an eyebrow. "What do you mean? I'm Izuku."

Momo scowled. "No, you're not! You– You're not Izuku!"

'Well, shit,' Marvin commented to Izuku. 'Looks like she knows you well.'

Izuku took over, and his shoulders immediately slumped in exhaustion.

"Momo… It's still me, ok? I'm just… I'm just tired," Izuku sighed, rubbing his neck.

Momo lowered her staff slightly, a knot in her throat.

The change was drastic. Izuku looked smaller than he was, and there was something about him that Momo couldn't quite put her finger on.

"I–Izuku, what was that?" She asked nervously. "That… Whoever that was, that wasn't you."

'We should tell her," Izuku stated. 'She already has a suspicion, and I don't want to lose her because of this.'

Marvin sighed. 'Fine. But we have to take it slow; if we reveal everything, it could overwhelm her.'

Izuku dropped his head, hand in his hair.

"Momo, I– There's something I have to tell you, but it has to be a secret," Izuku told her, staring at the ground. "Please?"

Momo's heart skipped a beat for a second but she quickly shook it off and nodded.

"Whatever it is, you can tell me," Momo promised. "I won't judge you for anything."

Izuku sighed and began explaining everything. From Marvin's appearance and learning they could switch– to the memories and nightmares they shared– and even how Marvin had taken over in most of his fights.

When it came time to explain the fights against Bakugo and the Nomu, Izuku's voice faltered, becoming a hoarse whisper.

Momo hugged him, resting his head on her and giving him comfort so he could keep talking.

He took the occasional pause and deep breath, and Momo squeezed him lightly whenever he did.

Izuku blinked as he ended his explanation.

They were sitting on the ground, backs against the wall, in a corner facing the door. Izuku hadn't even realized when they'd gotten there.

Momo was silently staring at the ground, chewing her lip lightly.

Izuku suddenly became aware of their proximity and blushed profusely, but didn't try to remove himself out of fear of seeming rude.

Marvin was glaring at him internally. 'You just HAD to go on and say everything, didn't you?'

'Sorry,' Izuku replied sheepishly. 'It just… It just spilled out.'

Marvin sighed. 'Whatever. I'm not dealing with her if she becomes overprotective of you, though. That'll be on you.'

"Izuku?" Momo asked, lightly poking his shoulder.

"Oh, sorry, were you saying something?" Izuku shook his head, trying to wave off the nervousness.

"Can I– You said his name is Marvin, right?"

Izuku nodded slowly. "Uhh… Yeah? Why?"

"May I speak to him, please?" Momo asked hesitantly. "I need to ask him some things."

"Uhh, sure," Izuku replied before letting Marvin take over.

Marvin sighed and rubbed his eyes. "You rang?"

He sat up as Momo let go of him, and pretended not to notice as Momo scooted away slightly.

"I'm not going to do anything to you, ok?" Marvin told her tiredly. "Just gonna answer your questions and Izuku's going to come back."

Momo stared at him for a moment. "How?"

"How what?" Marvin replied. "You're going to have to be more specific."

Momo blinked. Even though he was in Izuku's body, Marvin definitely didn't act like Izuku, and even the voice was different, being rougher and more mature-sounding than Izuku's.

She didn't know how she hadn't noticed it before and silently berated herself for it.

"How did you get into Izuku's body?" Momo clarified. "And… And how am I only now realizing this?"

"No clue and I imitate him very well," Marvin answered, staring at the ground. "The whole point was for nobody to notice anything, though I'm more than certain that some people may have noticed something off already."

Momo blinked and tilted her head. "What do you mean?"

Marvin shrugged. "Aizawa probably noticed, for one. He seems perceptive. All Might too, given he knew Izuku before I got here. Nezu's uncertain, but given how he spoke to Izuku after the Trials, maybe."

"No, I mean like… What do you mean you have no clue?" Momo asked. "You don't know how you got into Izuku's body?"

"Nope," Marvin replied. "Got amnesia from whatever sent me here, could barely remember my name when I showed up. Haven't remembered what brought me here yet."

Momo was tempted to ask what he did remember, but the way Izuku had spoken of their nightmares stopped her.

"Any more questions?" Marvin asked, looking at the wall above her.

"You aren't that polite," Momo pointed out, unsure what else to say.

"That isn't a question.," Marvin snorted. "I asked if you had any more questions."

"Why?" Momo blurted out. "Why aren't you polite?"

Marvin sighed and rubbed his eyes. "Cause– Cause I'm just an asshole, ok? Anything else?"

He stared at her and Momo leaned away slightly from his gaze.

His eyes were dead and cold, anger bubbling underneath. But it wasn't anger at her, rather, it seemed like anger in general, as if he were upset constantly.

"What is it, really?" Momo questioned softly.

Marvin raised an eyebrow. "Elaborate."

"I know you're not– not what you call yourself," Momo said. "Izuku said you helped him fight and defended him against Bakugo. If you were what you say you are, you wouldn't do that."

"It's called a mutual transaction, ok?" Marvin told her gruffly. "Helping him fight increases his chance of survival, and thus, mine. And defending him against Bakugo was just the normal thing to do."

"Chance of… Survival against what?" Momo did a double take. "What is there to survive?"

"Life!" Marvin snapped. "There's fucking thousands of things that can kill you out there and I'd rather not see him dead!"

"Just look at yesterday!" Marvin ranted angrily. "Stupid fucking mutant freak-looking thing, the product of genetic experimentation specifically designed to kill All Might! Sent to kill us. Sent to kill Izuku. If that isn't reason for his training then I don't know what is."

"And that's not to mention what happened with you," Marvin gestured to her. "You were dead on your feet and the others were halfway there! If we'd been quicker with killing that damn Nomu, then that wouldn't have happened!"

Momo blinked in shock, unsure how to respond. Marvin seemed to be talking from experience, his words more similar to some of the Pro Heroes Momo had met than a student.

Marvin took a deep breath. "There's no reason to believe the world is safe or protected, especially not yours. You're Pro Heroes who will be risking their lives, day in and day out. It's idiotic to believe there's no risk of death."

"You care about him, don't you?" Momo inquired. "About Izuku."

Marvin stared at the ground. "Care won't save him," He told her softly.

"There are dangerous things out there. If I can prepare him for them– make him more likely, or even certain, to survive– then that's all that matters."

"But you can't live if all you do is survive," Momo said. "He has to live too."

Marvin stared at her oddly, wondering where she'd gotten that tidbit of wisdom from.

"My mom said that to me," Momo supplied, seeing his look. "She was a Pro before she married my dad."

Marvin nodded in acknowledgment, returning his gaze to the ground.

"Smart woman," He said, rapping his nails against the floor. "Reminds me of someone."

Momo tilted her head in confusion. "I thought you didn't remember stuff from before you met Izuku?"

Marvin shook her head. "I didn't. I still don't remember much, but I'm remembering," He explained.

"That quote… I had someone who always told me to live, and not just survive," Marvin said, voice hollow.

"Really? What happened to them?" Momo asked.

"They died."

"Oh."

Marvin sighed. "Sorry, it's just– forget that people aren't as calloused as I am. Kind of a good thing, honestly."

Momo looked at him oddly. "What do you mean?"

Marvin snorted before looking Momo in the eyes.

"Look at me and tell me you'd want to be anything like me," He said, pointing to his eyes.

"Exactly," He said after Momo shifted uncomfortably but didn't answer.

They stayed silent for a bit, Momo not knowing what else to ask, and Marvin not quite caring.

After a while, Momo blinked, suddenly remembering something Izuku had said.

"Hey, Izuku said you helped him with fighting and everything," Momo began. "Does that mean you can use his Quirk too?"

Izuku and Marvin held a quick mental conversation before Izuku took over.

"Uhh, yeah, yeah he can," Izuku told her, rubbing his neck. "And speaking of… Momo, you know how All Might's training me and stuff?"

Momo arched an eyebrow, pieces beginning to click in her mind.

"Are you actually All Might's successor?" She asked.

Izuku flushed. "Yeah… I– I have his Quirk."

Momo blinked, her face quickly morphing into shock, and Izuku's eyes widened as he realized what he just implied.

"Not– Not in that way!" Izuku said quickly. "He's not– We're not related!"

"Oh," Momo said, calming down before her brows furrowed. "Wait…"

"He gave me his Quirk," Izuku told her. "I– I didn't have a Quirk before coming to UA."

"You're– Huh?" Momo asked intelligently.

Izuku explained how he had met All Might, All Might's words before and after defeating the sludge villain, his training, and how he'd inherited All Might's Quirk just hours before the Entrance Exam.

In the end, Momo was floored, completely unable to respond.

She thought Izuku had just been a late bloomer, or that he had a hyper-powerful Quirk he still hadn't grown into yet; it wasn't impossible for that to happen, just rare.

She began pacing, hands on her head.

"Are you alright, Momo?" Izuku questioned, staring at her.

"It's just– hold on, is that why All Might always refers to you first?" Momo asked.

"Huh? What do you mean?"

"Whenever there's a few of us together, All Might always refers to you first," Momo elaborated. "He did it in the Battle Trials and yesterday in the USJ."

Izuku blinked. "Huh, I didn't notice that before. I guess so."

"So, you're not only the successor to the World's Greatest Hero, but have his Quirk, and are almost certainly going to be as strong as him?" Momo questioned, rubbing her temples.

"Uhh, yeah? I guess so," Izuku rubbed his neck. "It feels kind of egotistical to say that, though."

Momo stared at him like he had gone crazy.

"Izuku, you're literally the successor to the Greatest Hero the world's ever seen," Momo exclaimed, exasperated. "All Might's presence alone dropped Japan's crime rate to 3%! He's been Number One for like, nearly 30 years!"

"Ah, well… I'm not really there yet, you know?" Izuku rubbed his arm in embarrassment. "I still have to master my Quirk, graduate UA, and work as a sidekick for a bit before I can climb the ranks."

"Oh yeah, you said your Quirk breaks you, right?" Momo asked, remembering what Izuku had told her a few days ago during one of their texts.

Izuku nodded. "Yeah. Marvin helps me with that. We managed to use One for All a bit longer yesterday when we found you guys."

"Wait… how does your Quirk break your body when you use it, but not when Marvin does?" Momo questioned. "Because I've never seen your Quirk hurt you when you fight."

"One for All still hurts me," Marvin explained. "I can just handle more 'cause I'm stronger. My Quirk transferred over to Izuku's body, but it can only be used by me for some reason. Well… he's never tried, but given it auto-activates whenever I'm in control, he probably can't."

"What's your Quirk?"

Marvin shrugged. "Strength and speed enhancement. Whenever I fought Bakugo, I wasn't using One for All, just my Quirk. Same thing for the Quirk Apprehension Test and when I killed that Nomu thing."

Momo stared at him in shock, her mind whirling as she processed that.

"You… All of that was without All Might's Quirk?!" Momo exclaimed. "But you were so fast during the Quirk test!"

"Don't know how strong I really am," Marvin replied, rolling his shoulder. "Seems to be connected to my memories. Don't know how exactly, but that's what I have so far."

Momo began pacing again, rubbing her temples with her eyes closed.

"SO, what I'm hearing is, neither of you is at full power, yet Izuku's easily one of the strongest people in the class already," Momo stated. "And you're training him to fight, which makes him stronger, and can also control his body if he's in trouble, giving him another boost?"

"Yeah, pretty much."

Momo sighed and rubbed her eyes.

"I'm not sure how to process this," She muttered. "I like that you're helping Izuku, but– isn't it weird being two people in one body?"

"If you're wondering, I don't spy on your convos," Marvin told her with a shrug.

Momo's shoulders relaxed slightly at that. "Oh, that's good."

"And at first, yeah. But we're slowly getting used to it," Marvin continued. "It's still disorienting sometimes, and it's uncomfortable for me personally. But we're managing."

"Uncomfortable?" Momo's brows furrowed. "Why?"

"It feels like a small box," Marvin explained. "From what little I could gather, I was bigger than Izuku in my normal body, and it seems like I remember that. Whenever I'm in control, it feels like I'm being squished into too-tight clothing, so I try not to take over for too long or outside of combat."

Momo hummed in thought. "Have you ever wondered about getting your old body back?"

"And tell me one way how to do that?" Marvin raised an eyebrow.

"You could tell the teachers," Momo pointed out. "The principal has a Quirk that makes him extremely intelligent. He could probably help."

"Yaoyorozu, I can control the body of someone with possibly the strongest Quirk in existence," Marvin told her blandly. "I can't remember anything, and I'm mostly only good at fighting. I've shown the capacity to kill and maim too– what do you think is going to be the first thing they do if they know?"

"Contain you?" Momo said almost immediately.

"Exactly," Marvin replied. "Not about to be locked in a cell and experimented on, and I'm not subjecting Izuku to that either. Either we'll find a way ourselves, or I'm forced out through some other means, but I'm not asking."

Momo stared at that. He wasn't exactly wrong when he put it that way, and she could definitely see why a possibility like that would be on the table.

"But– But All Might's also a teacher," Momo insisted. "There's no way he would do something like that!"

"And how exactly is he going to help us?" Marvin raised an eyebrow. "You're forgetting that this is a completely undocumented experience. Can't exactly look up how to do it, you know?"

The conversation continued for a while longer, though with Izuku and not Marvin, seeing as the latter was beginning to feel uncomfortable in the former's body again.

Once they said their goodbyes, Izuku felt significantly lighter than he had when he entered.

Momo had agreed to keep One for All a secret and had reinforced her decision to help him train, though she needed his promise to not use his full power against her, to which he readily agreed.

It felt odd, telling her and her accepting. If anything, she seemed more freaked out about Marvin than she did One for All.

But the important thing was that she knew now– he had someone to confide in and trust, just like Nezu had said.