Devil Fruit System in MHA

"Those are interesting. Both have a ton of potential in the hands of modern heroes," Nezu said, analyzing the fruits with keen interest. "The Warrior Fruit is clearly the leader in Limelight Heroics, but the Puzzle Fruit is far more versatile. I can see uses for it in Limelight, Underground, and Rescue heroics. While I'm grateful and not at all diminishing your gift… I admit, I wish I could have another. The Puzzle Fruit is so tempting."

As Nezu spoke, something clicked for Kai. Nezu Fruit Capacity Voucher flashed in his mind; a reminder stashed in his inventory.

Kai nodded, putting on a thoughtful expression. "Actually… my quirk might allow me to work around that limit, sometimes. I think I can, on rare occasions, authorize' someone to wield a second fruit. It's risky, and I've only just discovered this, but if it works, you could try the Puzzle Fruit without losing anything you already have."

Nezu's eyes widened, his interest sharpening. "Oh? I thought the one-fruit limit was a hard rule."

Kai threw his hands up in mock frustration. "I did too! But when I thought about giving you the fruit, my quirk just… gave me this feeling, like, 'sure, go ahead.' I have no idea how it works!"

Nezu chuckled, intrigued. "Then let's test it."

With that go-ahead, Kai selected the Puzzle Puzzle Fruit, and it materialized from his quirk's energy, springing forth from his hand. The fruit had an intricate, unusual appearance—its skin was patterned with interlocking puzzle pieces in shades of deep blue, silver, and gray, giving it a metallic, almost mechanical look. Shaped like a large apple, it had small, distinct ridges where each "puzzle piece" interlocked, making it seem as if it could be taken apart and reassembled.

As he plucked the Puzzle Puzzle Fruit, Kai reached into his inventory with his other hand, grateful that Nezu, in his human transformation, had only human-level senses. He pulled out the Fruit Capacity Voucher—a slim, talisman-like slip of paper adorned with a faint plus sign and an indistinct fruit symbol, encircled by tiny, intricate magical runes.

As he held it, a system panel appeared before him:

Would you like to use the Fruit Capacity Voucher on Nezu?

Yes, Kai thought firmly, handing the newly created fruit to Nezu.

Nezu inspected the fruit with a mix of curiosity and caution. "And you're sure that eating this won't harm me?" he asked, a hint of hesitation in his voice.

Kai gave him a reassuring smile. "Absolutely. I'm not sure what changed, but it's almost like I can sense an extra capacity in you for another Devil Fruit."

Nezu seemed comforted by the assurance and took a thoughtful breath before leaning in, then took a bite out of the Puzzle Puzzle Fruit.

Nezu took a careful bite of the Puzzle Puzzle Fruit, face contorting In disgust at the absolutely abysmal taste.

"I regret to inform that the flavor decidedly does not improve the second time." Nezu said, gagging. "But I do believe it has worked. I can, for the lack of better terminology, fell a kind of 'energy' underneath my skin, centering on my hands."

Kai chuckled at Nezu's reaction. "Yeah, Devil Fruits don't exactly come with a warning about the taste. But it sounds like it's settling in."

Nezu examined his hands with keen interest, flexing his fingers experimentally. "It's strange—this energy feels both foreign and natural, like it's always been there, waiting to be activated."

Testing his new ability, Nezu reached into his pocket, pulling out a paperweight. With a mere thought, the object's surface rippled, and in an instant, it disassembled into floating puzzle-like pieces, each hovering in place as though held by an invisible force.

"Fascinating," Nezu murmured, a look of pure delight spreading across his face. "It responds instantly to my intent." With a slight motion, he reassembled the paperweight, setting it back into his pocket.

Kai looked confused. "Why did you have a paperweight in your pocket?"

Nezu chuckled. "For combat of course! They're made with one of David Shield's proprietary technologies. They're roughly ten times the density of normal weights."

Kai blinked, then laughed, unable to hold back his amusement. "Only you, Nezu. Of course, your paperweights are secret weapons."

Nezu smirked, his eyes gleaming with mischief. "Preparedness is key, Kai. One must be ready for any situation, even if that means carrying something as deceptively simple as a weighted paperweight." He gave the pocket a pat as if to reassure its presence.

Kai shook his head with a grin. "If course. Literally everything on your person is lethal in some way, isn't it."

Nezu just grinned.

~~~~~~~~~~~~~~~~~~~~~~~~~~~

Gran Torino eyed Izuku criticallym, stretching out his arms and hands as he hopped from one foot to the other on his short, sturdy legs. They were standing in the heart of Ground Gamma, a maze of industrial pipes and platforms towering above them. The cool, metallic smell hung thickly in the air, and the quiet hum of machinery set the backdrop.

"So you're the Ninth, huh." Gran Torino said appraisingly.

"N-N-Ninth? W-What do you mean sir?" Izuku asked, panic absolutely coating his features.

Recovery Girl, who followed them for the sake of maintaining Izuku's bones, interjected. "He knows about One For All, Izuku. The Seventh told him."

Izuku's eyes went wide, and he fumbled through the air, summoning a notebook adorned with a pink seven from the endless supply he somehow kept on hand. "You-knew-the-seventh-wielder-what-were-they-like-what-was-their-Quirk-how-did-OFA-affect-them—"

Gran Torino raised an eyebrow, watching the rapid-fire questions with mild amusement. He waited for Izuku to pause for breath, then cleared his throat sharply.

"Well, at least Toshinori picked a smart one," he grunted. "The Seventh… she was stubborn. Had the same spark in her eyes as you—just a bit less... jittery." His gaze softened, a rare, distant look crossing his face. "Her Quirk? Float. She was good with it, too, especially once One For All boosted it. Helped her stay ahead when things got rough."

Izuku's pencil skittered excitedly across the page. "So One For All enhanced her Float—what did that mean, exactly?"

Gran Torino smirked slightly. "Supercharged it. Before OFA, she could levitate a few feet off the ground, maybe three or four. But with OFA?" He tapped his chest, recalling. "She could fly. And fast, too—almost enough to keep up with me in my prime."

Izuku's pen raced across the pages, leaving a faint trail of smoke. "Does that mean OFA's stockpiled energy bled into her Quirk? Or did they merge? No, if they'd merged, All Might would've had the Quirk himself—or at least some form of it. So, Float probably just fed off the energy reserves, which allowed—"

A sudden movement pulled him out of his thoughts. Almost unconsciously, Izuku swiped at the air beside him, instinctively channeling 5% of One For All into his arm. It wasn't until he heard a groan behind him that he realized what he'd done. He blinked, snapping back to reality, and looked up from his notebook.

Gran Torino lay sprawled out on the floor, grimacing.

Izuku's eyes widened in panic as he rushed to his new mentor's side. "Gran? What happened? Are you okay?"

"Yeah, yeah you whippersnapper. I've taken worse hits, just not in a while. I have to say though, your control is better than I thought it was. I was told you were breaking your limbs every time you used the quirk?"

Izuku blinked, and his brows furrowed in consternation. "What do you mean? I was just thinking about Seventh's quirk and heard you groan in pain."

Gran Torino grunted as he sat up, rubbing his shoulder. "Just thinking about it, huh?" He gave Izuku a skeptical look, eyebrows raised. "Kid, you're telling me you didn't even realize you'd swung?"

Izuku's face twisted in confusion. "No, sir! I was just… thinking. I didn't mean to… actually do anything."

Gran Torino waved a hand dismissively, a small smirk on his face. "Well, that's on me. Should've known better than to poke a ticking time bomb. Alright, enough talking—activate One For All. I want to see just how far you've come."

Izuku eagerly agreed, desperate to change the topic. He stepped over to a less cluttered area and released a deep breath. He flipped the switch to activate OFA and pushed the energy down into his legs, careful to keep the input limited. It was difficult, the Quirk did not want to be limited to such a small quantity and area, but he managed to do so after a few seconds of concentration. His legs were soon wreathed in green lightning and his skin started rippling where the aura was thickest.

Izuku released a shuddering breath, crouched down to the ground, building both strength and anticipation, and leapt. He launched himself ten meters in the air straight upward, soaring past the complicated web of pipes. He reached the apex of his jump roughly a third of the way through the pipes and started plummeting back towards the ground.

He started panicking, apparently not having thought about the consequences of such a leap. Luckily for him, Gran Torino swooped in and caught him before he could slam into the ground and shatter his tortured bones.

Unluckily for him, Recovery Girl watched him pull that stunt.

Gran Torino set Izuku down gently, his hands gripping his shoulders for a moment longer than necessary. "You know," he said, his voice tinged with amusement, "you've got guts, kid, but you've got to think these things through first."

Izuku, still wide-eyed from the near-miss, nodded rapidly, unable to form words. He opened his mouth to apologize, but before he could, a familiar voice rang out.

"Midoriya." Recovery Girl's voice was calm, but there was a sharp edge to it. "What in the world were you thinking?"

Izuku turned toward her, his face flushed with embarrassment. "I-I just wanted to test my limits with OFA, but I didn't think about how high I'd go—"

"Clearly," she interrupted, folding her arms across her chest. "You're lucky Gran Torino was quick on his feet. I don't know what's more troubling: your lack of foresight or your inability to listen when I tell you to be careful. If you'd gotten injured, you would have wished you were unconscious." The tiny lady swung her staff, pantomiming bashing his shins.

Gran Torino smirked, tapping his foot lightly. "Give the kid a break, Recovery Girl. He's learning. Just might need to tone down the ambition a little."

Izuku, still trying to get his bearings, finally managed to speak. "I-I'm sorry, Recovery Girl. I'll be more careful next time. I didn't mean to cause any trouble."

Recovery Girl gave him a long, assessing look. "Just don't make a habit of it," she said with a sigh. "Your bones can't take that kind of stress. I swear, you're just as reckless as All Might was at your age."

Izuku winced at the mention of his idol, but there was a faint sense of pride mixed in with the worry. "I'll work on it, I promise."

"You said that after the Battle Trials. And the Quirk Assessment Test. And the Entrance Exam. At this point, don't make promises you don't plan to keep."

Izuku's face flushed with embarrassment, the weight of Recovery Girl's words sinking in. "Sorry…"

"Apology accepted, for now."

"Well, as interesting as this little byplay is, I do have a question for you Izuku. Why are you limiting OFA?" Gran Torino asked, eyebrow cocked.

Izuku looked confused. "Because if I go above my limits my bones break? It's been proven quite a few times."

"I didn't mean power, I meant activation. When you did your cannonball act you only put the quirk in your legs. Why?"

Izuku just looked more lost. "Because I was using my legs?"

Gran Torino stared at him for a moment, a small smirk tugging at the corner of his lips. "Yeah, that's the obvious reason, but there's more to it than that. You can activate One For All in different parts of your body, right? You don't just have to focus it in your legs or your arms. You can control where it goes, which means you could potentially avoid overloading any one part of your body."

Izuku blinked, still not fully grasping. "So, you're saying I don't have to use OFA in just one place at a time?"

Gran Torino nodded, walking around him, the short, rhythmic sound of his footsteps echoing in the silence. "Exactly. If you distribute the power more evenly, you can reduce the risk of overexertion. Your body's just like any other—it's all about balance. You don't have to throw everything into one punch or one leap. OFA isn't just for Super Moves."

"I think I get it? You're saying I should keep it active instead of using it for bursts."

Gran smiled. "Now you're getting it. Try spreading it throughout your entire body."

Izuku took a deep breath, feeling the weight of Gran Torino's words settle in. He had always viewed One For All as a tool for explosive bursts of power, focusing it into one spot and unleashing it all at once. But now, Gran was suggesting something different—something more refined.

He closed his eyes for a moment, concentrating. This was a whole new level of control. Slowly, he activated OFA, but instead of just focusing it in his legs or arms, he tried to distribute the energy across his entire body. He imagined the power flowing from his core, into his arms, legs, chest, and even his fingers, all working in harmony. The familiar green lightning crackled around him, but it felt less intense, more evenly spread out.

Izuku could feel the difference immediately. His muscles didn't feel overloaded, and his body didn't tremble under the strain. It was as though he could actually use the power rather than just survive it. He opened his eyes and, with a tentative step forward, tested the new method by moving.

It felt... effortless. A smooth flow of energy coursing through his limbs as he took a few more steps, each one more confident than the last. He moved around, pacing back and forth, testing the limits of his new control. The power didn't surge, it simply was, steady and contained, like a river flowing through him without threatening to burst its banks.

"I— I think I've got it!" Izuku said, his voice was a mix of awe and excitement. "It's like the power's... working with me, instead of pushing me!"

Gran Torino watched him closely, a small nod of approval in his eyes. "Good. Now, try jumping again. But this time, spread the power out through your legs, your core, everywhere. Don't hold back, but don't focus it all on one area."

Izuku took a deep breath and then jumped. It felt so much different than last time that he couldn't even compare the two accurately. The first time felt like he was shot out of a cannon, lacking any control and unable to process anything. This time he felt like he was truly in control. He felt himself falling through the air back to the ground and simply used a couple of the pipes around him to descend safely.

"That… was amazing." Izuku exhaled, releasing his quirk.

"That it was. Now its time for part two. Maintaining control while sparring." As Gran said this, his face slowly morphed into a sadistic grin.

Izuku's stomach dropped at the sudden shift in Gran Torino's expression. The grin that spread across his face was anything but reassuring. Izuku felt a nervous chill crawl up his spine as Gran's eyes gleamed with a mischievous spark.

"Sparring?!" Izuku echoed, the apprehension in his voice palpable. "I-I'm still getting used to the control! I thought we were working on that first!" He backed up a few steps, his mind racing at the thought of facing off against Gran.

Gran chuckled darkly, his small stature somehow making him appear even more menacing. "What better way to test control than in the heat of battle? You need to learn to balance your power when you're under pressure. This isn't just about fancy jumps and calculated moves—this is about surviving a real fight."

Izuku took another step back, unsure whether to be more scared of the sparring or the look in Gran's eyes. "But... Gran, I don't know if I can—"

Gran didn't give him a chance to finish. With a swift, almost imperceptible motion, he darted forward, moving faster than Izuku had expected. His hand shot out, aiming for Izuku's stomach with a surprising burst of speed.

Izuku didn't dodge in time and took the hit right in the gut, curling over and clutching his stomach.

"C'mon kid. You need to learn how to keep that quirk active in combat, otherwise you have learnt nothing. Now fight back!"