I do not own Katekyo Hitman Reborn.

Summary: I-Pin and Lambo have no recollection of Tsuna's old teacher, Nezu. But he remembers them, and when they become his students, he goes out of his way to make their lives miserable. He will come to greatly regret this decision when Reborn discovers what's going on.

Nezu's Grudge

"I-Pin-chan, Lambo-kun! Breakfast is ready!"

A minute later the two seven-year-olds appeared in the kitchen, dressed in their school clothes. I-Pin's raven hair was tied into a neat braid and she wore a crisp white blouse with a dark blue skirt. Lambo wore a similar outfit, with a shirt and pants. He looked far less enthusiastic than his best friend, a pout on his lips and fingers tugging insistently at his collar.

"Thank you Mama," the two chorused, taking their seats.

"You two are just adorable," Nana cooed, looking upon them with pride. "I'll have to take a picture before you go."

"Aw, you really don't have too," said Lambo with a wince.

"Don't argue with Mom, Lambo," chided Tsuna, coming into the kitchen in his own school uniform. He grabbed a piece of toast from the plate and took a quick glance around the table. "Futa!" he called when he discovered the boy missing. "You're going to be late for school!"

"We'll be right down!" responded Bianchi, her voice drifting from upstairs. "Futa's got a bit of a hair problem."

"A hair problem?" echoed Tsuna in bafflement. "He's ten. He's too young to worry about his hair."

"Hair is very important," informed Lambo seriously, who liked his mass of raven curls very much.

"You probably wouldn't care so much if you weren't able to hide stuff in that nest," said Tsuna in amusement. He then added, "Stop pulling at your collar."

"But it's itchy," he whined, reluctantly lowering his hand and moodily shoving some rice and egg into his mouth.

"We'll wash it tonight, Lambo-kun," promised Nana, pouring herself a glass of juice. "It'll be more comfortable once you work it in."

"Stop complaining, stupid cow."

Lambo yelped slightly when a fistful of his hair was pulled. He craned his neck to glare up at Reborn, who stared impassively back. "I'll complain all I want, stupid Reborn!"

It was still a bit of a shock that the tall, imposing adult before him was once the infant he had been tasked to kill. The Arcobaleno curse had been broken by Tsuna when he was fourteen and it was only recently that Verde came up with a solution to restore their ages back to what they were before they were cursed. Nana, who had been informed of her family's Mafia lifestyle and connections, accepted Reborn's transformation with open arms, proving what the hitman had always suspected. She was a stronger woman than people gave her credit for.

Rolling his eyes, Reborn gave the back of Lambo's head a sharp swat before moving to take his seat. Bianchi came down a few minutes later with Futa, whose cowlick was finally under control thanks to the woman's skill with hairspray. They ate their breakfast and soon Yamamoto and Gokudera arrived to walk with Tsuna to school.

"Bye, everyone!" said Tsuna as he grabbed his bag. He gave his little siblings each an embrace. "See you three later. Be good at school today."

"We will if you will," said Futa cheekily.

Tsuna gave him a playful glare before rushing out to join his friends outside. It was another few minutes later when Futa, Lambo and I-Pin were ready to go. They endured through some pictures for Nana and set off on their way. They made it to Namimori Elementary with time to spare and separated to go to their respective classes. Lambo and I-Pin walked into their second-grade classroom, where the rows were two desks wide.

"Come on Lambo, cheer up," spoke I-Pin, taking a seat beside her best friend.

"I can't," said Lambo miserably. "I hate school."

"It's not so bad. It can be fun."

"Sure, until we have to do homework and Reborn has to tutor me."

There was the sound of intermingled chatter as other second-graders filed into the room and took their seats. The bell rang, signalling the beginning of the day. A raven-haired male walked stiffly into the room, taking his position behind the teacher's desk.

"Quiet down!" he instructed sharply, and the lingering conversations immediately halted. "You are now second-years, another step up the academic ladder! I am Nezu-sensei. I will engrain in you good study habits that will take you through the rest of your academic career. There is no room for laziness or sloppiness! Am I understood?"

His students blinked at him, expressions ranging with various levels of confusion at his passionate speech. "Hai, Nezu-sensei," they all chorused.

"Good." Satisfied with their answer, Nezu removed his clipboard from his briefcase. "Before we have our class meeting, I will go through the class list."

As he began to read off the names, I-Pin leaned close to Lambo and whispered, "Doesn't he look familiar?"

"Not really," said Lambo in a bored voice.

"It feels like we've seen him before." Brow furrowing, I-Pin could not place their new teacher, though there was no doubt that she recognized him from somewhere.

"Bovino Lambo."

As Nezu read off the name, he glanced up in time to see the boy raise his hand and say, "Hai." Their eyes locked and the man gave a start. His eyes widened behind his glasses as he stared at the child, whose bright green eyes and curly hairstyle sent a sharp wave of remembrance through him. He could hear the cackle in his ears, the loud obnoxious voice.

For a moment, he thought he was perhaps imagining things, but then he turned his head and spotted the girl sitting beside Bovino. He then knew without a doubt that these were the two brats that had often infiltrated Namimori Middle a few years ago—the two kids who were closely tied with Sawada Tsunayoshi.

Eyes narrowing, Nezu went on to the next student, but the room seemed to chill by several degrees as he levelled the two with a glare. Shrinking slightly in his seat, Lambo did not miss the resentment the practically radiated in their direction.

"Er…yeah, we probably have seen him before," he said under his breath. "And whatever happened, I don't think it went so well."

Lambo's assumption was proven as the day went on. Whenever Lambo whispered something to I-Pin, he was snapped at by Nezu for talking during class. Whenever I-Pin tried to remind Lambo to practice writing in Japanese instead of his native Italian, she too was yelled at. Lambo bristled during each reprimand as their classmates snickered and could no longer keep his mouth shut during science period.

"Can someone name the process that is used when a particular species of insects changes form?" asked Nezu.

Nakada raised his hand and answered, "Metamorphosis."

"Correct. What is the precise definition of metamorphosis?"

I-Pin raised her hand. "Metamorphosis is when—"

"I don't believe I called on you," interrupted Nezu coldly. "I don't appreciate disrespect in my classroom."

"Hey!" exploded Lambo, unable to keep quiet at the way I-Pin shrunk beside him. "You didn't call on Nakada-san either but you let him answer!"

"I gestured to him," said Nezu with a scowl, "as you would have noticed if you were paying attention."

"I was paying attention," defended Lambo. "You were looking at your textbook when Nakada-san answered your question. You didn't point at him or anything."

"Are you accusing me of lying?"

Dark eyes wide, I-Pin nudged her friend's foot beneath the desk, a silent plea for him to keep quiet. But she should have known better, for Lambo glared at Nezu and said strongly, "Yes. I am."

"Detention for you both," he hissed between clenched teeth. "Perhaps writing some lines will drill some much-needed character into you."

This, thought I-Pin miserably, is the worst first day of school yet.

…

Their fingers cramping from writing over three dozen lines, Lambo and I-Pin left Namimori Elementary an hour after the dismissal bell rang. Massaging her sore digits, I-Pin was surprised to see Futa sitting on one of the metal benches stationed along the stone pathway. His nose was buried in a book and she called his name to get his attention.

"Hey," greeted Futa, lowering his novel. He regarded the two with a frown. "Please don't tell me you got detention on your first day."

"Yes," grumbled Lambo, shaking out his hand and tears gathering in the corners of his eyes from the pain. "Our teacher is a jerk!"

"That's not nice to say," scolded Futa lightly. "What happened?"

I-Pin explained the story and the ten-year-old mulled it over. "Well," he began, "that is unfair. But maybe it was just a misunderstanding. I'm sure things will be better tomorrow. Teachers aren't supposed to pick on their students."

"Doesn't mean they won't do it anyway," grumbled Lambo.

"Have you ever had Nezu-sensei before?" I-Pin asked.

"No," said Futa with a shake of his head. "I haven't."

"Lucky."

"What are we going to say to explain why we're late?" I-Pin asked her best friend.

"Not that we got in trouble," said Lambo firmly. "I'll think of something."

They walked home, where they made it in time for supper. They quickly changed out of their school clothes and into casual attire before joining their family at the dinner table. Stirring his Miso soup around, Tsuna glanced over at his little siblings with a slight frown.

"Where have you guys been? School ended an hour ago."

"We went to play in the park," lied Lambo. He did not want Tsuna to know he had gotten detention on his first day of school. He would be disappointed and Lambo hated it when his brother was disappointed in him.

Nana and Bianchi asked the kids about their day, with Tsuna and Futa fielding most of the questions. Lambo and I-Pin piped up every so often, but their responses lacked any real enthusiasm. I-Pin was conscious of the obsidian stare that Reborn directed at her and Lambo. He did not say anything, but she suspected he didn't quite believe Lambo's excuse for being late.

Her suspicions were confirmed after dinner, when everything was cleared from the table and the two seven-year-olds were in Lambo's room. She was reading through her notebook, reviewing the notes while Lambo lazily flicked through a manga. They both immediately felt Reborn's dominating aura before the man even appeared.

Leaning against the doorframe, arms crossed over his chest, Reborn surveyed the two. "For three kids who went to play in the park after school, your school clothes were remarkably pristine," he drawled.

Lambo's eyes flared defensively and Reborn could practically see the wheels turning in the boy's head as he formed a counterattack. For a brief instant I-Pin's eyes shifted guiltily before settling back on the one addressing her.

"Mama tells us to be careful when we play in our good clothes," returned Lambo. "So that's what we did."

"Don't get smart with me, idiot cow." He landed a swift kick to Lambo's side, sending him flying off the bed. His angry cries were quickly cut off when a heavy foot landed on his chest. "You can't even eat breakfast without spilling something. There's no way in hell you roughhoused at the park without getting a single speck of dirt on you."

"Ow, ow, ow, ow!" cried Lambo, tears falling down his cheeks. "Get off, stupid Reborn!"

I-Pin eyed the two with amusement, which quickly flickered out when Reborn trained his attention on her. "When you let him do all the talking, you're up to something." Ignoring the insistent smacks Lambo gave his ankle in an attempt to dislodge his foot, the hitman merely increased the pressure. "I detest lying."

I-Pin flinched at that. "Okay, we didn't go to the park," she admitted, playing nervously with the hem of her red shirt. "We got detention. Futa was just waiting for us and he went along with Lambo's story."

Annoyed, Reborn relinquished his foot, allowing Lambo to sit up and rub at his chest. "You got detention on your first day of second year," he said slowly, "and tried to cover it up."

"We didn't want Sawada-san to be mad at us," said I-Pin softly. "We didn't mean to get detention. It was my fault."

This caused Reborn some pause, for it was rarely ever I-Pin who landed the pair into trouble. "Oh really?" he said with a raised brow. "Explain."

"I didn't wait for the teacher to call on me before I answered his question."

His lips sharpening into a frown, the man asked incredulously, "You received detention for that?"

"Yes. But it's okay. I shouldn't have been rude."

Not at all content with the drastic punishment (only he could deal out harsh consequences to them), Reborn turned to stare down at Lambo. "How did you get detention?"

"It wasn't fair that I-Pin got in trouble for a dumb thing like that," he muttered.

"So you talked back."

"Yeah."

The smack the child received was lighter than usual, though he didn't notice. Reborn approved of Lambo standing up for his best friend, who certainly faced an unfair punishment. "You need to learn to watch your mouth," he warned the sulking Lambo. He swivelled to stare at the miserable I-Pin and added, "I know it was a mistake, but you know better. Remember to wait to be called on before you speak in class."

"Hai," said I-Pin with a nod. "I will."

"Are you gonna tell Tsuna-nii?" asked Lambo.

"Tch. He's got enough to worry about without adding the trouble you hellions get into at school."

Smiling in relief, I-Pin said gratefully, "Thanks Reborn-san!"

"Ah, thanks, stupid Reborn."

"You won't be so happy if you get another detention this month," said Reborn silkily. "If that happens, you answer to me."

Lambo made a face and I-Pin quickly said, "Hai!"

Reborn smirked and departed. Though the two would certainly find themselves in trouble if they got another detention, their teacher would be fearing for his life if he punished the two for any more unintentional mistakes.

Waiting until the door shut firmly behind the hitman, I-Pin turned to her best friend and said uncertainly, "Maybe we should have told him the whole story."

"He's always telling Tsuna-nii to deal with stuff by himself," replied Lambo, crawling back into his bed. "He'd probably tell us the same thing." His gaze hardened with resolve. "We don't need stupid Reborn's help anyway. We can handle this. All we have to do is not get into any trouble."

I-Pin squinted at him. "Who are you and what have you done with Lambo?"

…

As the month of April progressed, Lambo and I-Pin did their best not to attract attention to themselves. But Nezu took every little opportunity to belittle and yell at them. If they walked into the class a second after the bell rang, Nezu lectured them for being late, ignoring the other students that trailed in after them. If Lambo spilled something at lunch, they were both forced to clean the entire classroom for being sloppy. I-Pin was scoffed at for giving a wrong answer and Lambo was scolded for participating in discussions too much.

Futa quickly realized that his friends were not over-exaggerating and urged them to tell Nana or Tsuna of Nezu's treatment. But Lambo was stubborn and would not concede defeat, and I-Pin was determined to become a perfect student so that Nezu would like her. She stayed up late studying, but no matter how much effort she put into her work, Nezu gave her low scores.

"I don't get it," she said one evening, miserably pouring over her paragraph she had written for a Japanese Language assignment. "How come he hates us so much?"

"I don't know," said Lambo bitterly, struggling through his math homework. After getting a dismal mark on his test, Nezu assigned him six pages of extra problems to do, which needed to be handed in tomorrow.

A sharp rap sounded on the door, causing the two to freeze. Without bothering to wait for an answer Reborn entered. "Oi, aren't you two listening? Mama called you for dinner."

Though the two kids were starving, they could not see how they could break for dinner and complete their homework before bedtime. Glaring at his worksheet, Lambo muttered, "Not hungry."

"Not hungry?" echoed Reborn, lips twitching into a frown. He moved to stand behind the child and took a firm grip of his neck, discreetly feeling for signs of a fever. "Has the bottomless pit finally been filled?"

"We have homework to do."

"It takes a solid thrashing to get you to do any work," countered Reborn. "Yet these past few weeks you have been holed in your rooms studying. I wish I could believe I-Pin has finally rubbed off on you, but I sincerely doubt even her studious habits are enough to penetrate your thick skull."

Huffing out a breath, Lambo hunched his shoulders. "I didn't do well on my math test, okay?" he grumbled. "I have to do extra sheets on top of the other homework."

"Where is it?" asked Reborn sharply, smoothly transitioning into 'tutor' mode.

Lambo reluctantly handed over his test, which Reborn surveyed. There were a few problems in which the boy had reached the wrong calculation, but not enough to warrant such a low mark. Many of the deductions were because Lambo had not followed every step in the process to reach the solution, many of which were correct.

Feeling that something was not quite right, Reborn looked to I-Pin. "What about you?"

"My Japanese Language paragraph," she said, handing it over.

Reading through it, Reborn realized that she too faced deductions for minimal and insignificant reasons. Her writing was neat and concise, and though she was not perfect with her choice of Japanese characters, it wasn't horrible.

"Does your teacher mark everyone this harshly?" he asked suspiciously.

I-Pin gave a helpless shrug. "I don't know. I haven't looked at the other assignments Nezu-sensei has marked."

The pure anger that pulsed from Reborn at this response cowed both of the kids. Hands digging into the paper, nearly tearing it into pieces, Reborn spoke through clenched teeth, "Who's your teacher?"

"N-N-Nezu-sensei," squeaked Lambo.

Thinking the hitman's fury was directed at her for doing poorly, I-Pin felt tears gather in her eyes. "I'm sorry. I'll do better next time, I promise—"

She halted in surprise when Reborn swooped down and took her chin in a steel grip, keeping their gazes locked together. "You don't have to apologize," growled Reborn. "Your paragraph is fine and so is the idiot cow's test. How long has Nezu been given you extra homework?"

"Since the second week of school," said I-Pin, awed by the intensity in Reborn's obsidian gaze. "If he thinks we didn't do good enough he gives us more homework."

Straightening, Reborn flexed his fingers, gathering enough self-control not to punch the nearest wall. "Has he been harassing you?" he demanded.

"He's…he's been picking on us," spoke Lambo hesitantly. "If we're a bit late he'll yell at us, but he'll leave anyone else who comes in late alone. He laughs at us when we answer a question wrong. He keeps us inside for recess sometimes."

"We think he hates us," added I-Pin quietly.

"The detention you had on your first day…you didn't tell me everything, did you?" Reborn's eyes narrowed. "So you're going to tell me now."

"I did speak before being called on. But the student before me did the same thing and Nezu-sensei didn't say anything. He got mad at me and said I was being disrespectful."

"He was mean," chimed in Lambo. "So I called him a liar and then he gave us detention."

"He's been mistreating you since the first day of school, yet you haven't said anything?"

I-Pin shrugged. "I suppose we thought he would stop," she said uncertainly. "We thought we could deal with it."

"I didn't want him to think I was a loser," muttered Lambo, rolling his pencil along the surface of his desk. "He's not the first one to treat me like garbage anyway."

Reborn threaded his fingers through the boy's raven curls and pulled lightly, guiding his forlorn green gaze up to meet his fierce obsidian. "The only people who get to thrash you around and insult you are the members of this family. Understand?"

The possessive, protective undertone of Reborn's cool voice caused Lambo to smile sincerely for the first time in weeks. "Yeah, stupid Reborn. I understand."

When I-Pin did not respond, Reborn turned to face her. "Do I need to repeat myself?"

Realizing that he had been addressing her as well as Lambo, the girl nodded hard. "I understand, Reborn-san."

"Good." Reborn hoisted the two kids to their feet and pushed them towards the door. "Go eat dinner. After, you can do your homework. Don't even think about doing the extra crap he assigned you."

"But we're going to get into trouble," protested I-Pin.

Reborn reached down and lightly flicked her forehead. "Never bothered you before, brat. Go. Don't make me tell you again."

"Aren't you coming?" asked Lambo.

"Tell Mama I'll be late. I've got an errand to run."

The two kids rushed off, feeling a bit happier and lighter now that they weren't dealing with their burden by themselves. Reborn strode after them, but instead of heading into the kitchen he went towards the front hall. He stepped into the evening air and began the trek for his destination, strides long and purposeful.

…

Sitting at his kitchen table, Nezu ate some rice as he read through a book. His peaceful meal was interrupted by a loud bang that reverberated throughout the house. Jumping to his feet, he raced for his hallway to investigate the noise. He came to a sudden halt when he discovered his door swinging off of its hinges.

"What's going on here?" he boomed.

He rushed outside, but could not see any sign of the vandals in the cool dark night. He went back inside his house and made tracks for his phone, intending to call the authorities. He froze in the living room entryway when he caught sight of the mysterious, sinister figure lingering in the shadows.

"Who—who are you?"

Unfurling from his casual position against the wall, Reborn kept his fedora low over his eyes. "You've been harassing my kids."

Nezu suddenly felt a cold weight in the pit of his stomach. He stared at the man intruding his living room, his yellow-striped hat sparking yet another surge of familiarity. It was the same hat that the weird infant that always followed Dame-Tsuna had worn.

Why is this happening?! Why are all these people from the past suddenly reappearing? I haven't seen them in years and here they are, back again to ruin my life!

His throat dry, Nezu cleared it before speaking. "Your kids?"

Reborn moved slowly, his actions reminiscent of a predator. "Not my kids solely. They belong to the rest of our family. If you don't answer my question, I'll bring the rest of them down here. I guarantee they won't leave you with all of your limbs intact."

Nezu paled. "I wasn't harassing them," he finally said. "I was correcting their poor character. They're disrespectful and lazy! At this rate they'll turn out just like Dame-Tsuna!"

The man was pinned against the far wall in an instant, Reborn's hand harsh against his neck. The lip of his fedora was raised, revealing obsidian eyes glinting with murderous anger. "First of all," he snarled, "very few people get to call Sawada Tsunayoshi by that nickname these days. Refer to him as such again and I will embed the lenses of your glasses into your eyeballs."

Nezu choked out a terrified gasp. "You're insane! Let me go!"

"You are in no position to give orders. You are, however, in a position to answer my questions. Give me one reason why you treat I-Pin and Lambo so terribly. A reason that in no way relates to Tsuna."

Pale and shaking, Nezu ground out, "It's what I said before! They're disrespectful and lazy!"

"No," said Reborn in a voice that sounded pleasant, but anyone who knew him would detect the danger beneath. "I-Pin is the hardest working and sweetest kid I know. Lambo may have a mouth on him and he constantly forgets his place, but he's a good kid. He knows bull when he hears it and he won't take it lying down. You are not a figure worth his respect and he knew it right away.

"You bully them because you know they're related to Tsuna. They're your only targets for your bitterness and your hatred. The student that humiliated you so long ago was never punished in your eyes and you were fired for falsifying your academic transcripts. It's all his fault for your incompetence, right? That you were never as smart or as accomplished as you always claimed."

Nezu choked as Reborn increased his pressure, fingers tightening around his throat. "The reason you never improved is because you weren't capable of it. There are people who can grow and mature into beings superior to their previous selves. You had reached your limitations and could never do any better. Tsuna was your greatest reminder of your failures and you projected your hatred onto him. But he was growing. He was improving. That left you furious, up until the day you were fired.

"You can hold this petty grudge of yours for the rest your life. I don't give a damn. But you will leave Lambo and I-Pin alone. They have nothing to do with your feud with Tsuna. They are in your class to get an education and you will give that to them. You will mark their work fairly. I will know, because I will review every single assignment and test you hand back. If I see any more hints of bias, if they tell me any more stories of how you mistreated them, I will come back. And I'll bring the rest of the family with me. I doubt you'll enjoy being fired a second time around—and you're probably fond of keeping your body parts."

Reborn retracted his hand, allowing Nezu to take gulps of air. He was white and trembling, only able to stand with the support of the wall. "I understand," he croaked, knowing without a doubt that this man would kill him if he did not comply. "None of this will happen again!"

"You better hope so."

And then with a solid punch to the center of the man's face, Nezu slumped to the ground, unconscious.

…

The next afternoon, Reborn lounged against the sofa in the Sawada residence. A newspaper was open in his lap and he did not look up when he heard two sets of small feet come up behind him. "You're late," he drawled. "Ten minutes, to be exact."

The aroma of fresh coffee reached his senses and he craned his head. Lambo proffered a cardboard cup of the beverage. He and I-Pin wore bright smiles, eyes shining with admiration and gratitude. "Thanks for talking with Nezu-sensei," chirped the girl.

"I don't know what you're talking about."

Lambo smirked. "So it's just a super coincidence that Nezu-sensei apologized to us this morning with a cast on his nose the day after we told you about his jerkiness?"

"Yes."

"Fine. No coffee for you."

Reborn easily plucked the drink from the boy's grasp. "I'll take it anyway, idiot cow. You have homework?"

"Yes. But he didn't give us any extra this time," answered I-Pin.

"Then do it. I'll be looking over every piece of marked work you get back, so you better have your grades up to my standards."

He offered no protest when Lambo and I-Pin climbed onto the couch on either side of him. I-Pin dutifully reached into her schoolbag and pulled out her science textbook. Lambo tried to turn the television on to watch cartoons, but a sharp flick to his ear from Reborn caused him to huff and moodily grab his own textbook. Taking a sip of the warm beverage, Reborn relaxed contently against the cushions. He listened to I-Pin's soft humming and Lambo's cheerful chattering.

If it was one lesson the world ought to learn, it was that if his kids weren't happy, Reborn wasn't happy. If Nezu had known this, he never would have spoken a word to the kids in the first place.