In the thirteenth year of the Konoha Village, the First Hokage passed away. At his funeral, Tobirama succeeded him as the Second Hokage and swiftly initiated sweeping reforms.
First, he publicly announced the establishment of the Ninja Academy. All children over the age of four could apply for admission.
Based on their entrance exam scores, they would be assigned to different classes.
Second, he formed an agreement with the Uchiha Clan to create the Konoha Military Police Force.
The current Uchiha clan leader would serve as the Police Force Captain, responsible for maintaining internal order and village stability.
In addition, Tobirama selected a group of elite shinobi to form a special assassination and tactical squad, known simply as the Anbu.
Their duties included espionage, assassination, interrogation, and high-level defense operations.
One morning in late autumn, Arima was dressed only in a thin training uniform, heading to the training field as usual.
Just a few days prior, Tobirama had handed him the scroll containing the Flying Thunder God Technique.
He had only just begun to grasp the principles of this space-time ninjutsu and still required intense practice.
Although he had accumulated more than 5000 virtue points, raising his mastery of the Flying Thunder God from beginner to expert would take a full ten thousand points.
Arima was naturally talented, he knew that with dedication and practice, his proficiency would soon improve.
Suddenly, a masked ninja wearing a mask with animal markings appeared not far from him.
Arima immediately recognized the man as a member of his grand-uncle's newly established Anbu.
Without hesitation, he dispersed the one-handed hand seal he had just formed inside his sleeve.
As the Anbu operative stepped closer, an overwhelming sense of danger shot through him, every hair on his body stood on end, as though he'd stepped into the predator's lair.
He was, by all standards, an elite young shinobi from another clan.
Although he had heard the Second Hokage praise this young Jonin many times, he harbored some skepticism and pride of his own.
So, he had purposefully approached within Arima's defensive range to test his reaction.
But the moment he stepped close, he was hit by a crushing sense of pressure. It felt exactly like when a helpless animal finds itself locked in the gaze of a top predator.
The feeling vanished in an instant, but he knew it wasn't an illusion, that oppressive force had definitely come from the ten year old standing before him.
In that moment, he had to admit it, the small-statured Jonin before him had the power to kill him.
In the world of shinobi, strength speaks louder than age. And now, Arima had earned his respect.
The Anbu bowed respectfully through his mask and said, "Lord Arima, the Second Hokage requests your presence."
Arima gave the man a glance, and in the blink of an eye, vanished.
That single glance brought the pressure back again. Only after Arima's presence had disappeared did the Anbu let out a long breath, feeling a chill run down his spine.
He thought to himself, No wonder both Hokages speak so highly of him... His strength is the real deal.
From the moment that Anbu stepped into his range, Arima had already guessed his intentions.
Though he was generally kind, he never tolerated provocation. Over the years, he had learned this was the most comfortable way to deal with people, be friendly, but not weak.
To Arima, this little encounter was barely a ripple, it passed and was gone.
Before long, Arima arrived at the Hokage's office. He knocked softly on the door and heard his grand-uncle's voice from within.
"Come in."
As he stepped into the room, he saw that the floor was covered with piles of paperwork, most of which were related to the three newly formed organizations.
When Tobirama saw Arima, the stern look on his face eased. He let out a long sigh and said, "Arima, I have an important mission for you."
Arima nodded. "Granduncle, just say the word. I'll give it everything I've got."
Tobirama waved a hand, a smile touching his lips. "Actually, it's quite simple, for you, at least. I want you to serve as the vice-principal and head instructor of the new Ninja Academy."
Arima, who had mentally prepared himself for a bloody battlefield assignment, was momentarily stunned.
Teaching?
That caught him completely off guard. Though he was a fast learner himself, it didn't mean he was confident in his teaching skills.
Seeing the doubt on his face, Tobirama explained directly, "You know your grandfather and I have high hopes for you. One day, the title of Hokage will be yours.
But for that, you need to learn more than just ninjutsu. You need to start experiencing the mundane, day to day responsibilities as well."
Arima looked into his grand-uncle's serious expression and remembered the dreams of his grandfather, the First Hokage. He fell into deep thought. Could he really handle this role?
Tobirama added, "Over the past six years, you've done a lot of good. The villagers recognize your character and your strength.
This role will also allow you to spot promising students and nurture future talent. Besides, if Tsunade knows you'll be with her at school, I think she'll be thrilled."
Those words made perfect sense. Arima no longer hesitated and accepted the appointment on the spot.
He also felt reassured by the idea of being able to stay by Tsunade's side, watching her grow.
When he first learned she would be attending school, he had actually worried she might get bullied.
The news of Arima's appointment spread quickly through the village. The people respected both his power and his character.
Meanwhile, when Tsunade heard the news from her grandmother, she was overjoyed. Finally, I can be with Arima-nii every day.
Mito watched her granddaughter's delighted expression and couldn't help but sigh in her heart.
Who would've thought that joke I made all those years ago with little Arima would actually come true?
But then again... it's probably for the best. The children should walk their own paths.
That night, when Arima returned home after his daily training, he found Tsunade fast asleep in his bed. Watching her peaceful, adorable face, a smile crept onto his lips.
He couldn't bring himself to wake her, so he carefully tucked her in, laid out a futon beside the bed, quickly washed up, and went to sleep.
In the middle of the night, he felt Tsunade kick off her blanket, clearly uncomfortable and close to waking.
He sat up and gently pulled her into his arms, softly humming a lullaby his mother used to sing.
Sensing Arima's presence, Tsunade clung tightly to his warm chest and mumbled a sleepy, "Arima-nii..." before falling back into deep slumber.
Arima's heart melted.
He gently moved her into his futon and held her close, softly repeating the lullaby as he drifted off to sleep.
The next morning, Arima was still half-asleep when he felt something soft and fragrant in his arms. He suddenly remembered, he had slept with Tsunade in his arms last night.
He opened his eyes wide and saw her staring at him with big, curious eyes.
He poked her nose playfully and yawned. "Tsunade, why are you up so early?"
Tsunade recalled waiting for Arima last night so they could head to school together.
He had come home really late, and she'd fallen asleep. All she remembered was him holding her and singing to her.
She asked, "Arima-nii, what time did you come home last night?"
Then, as if catching his yawn, she let out a huge one of her own.
Arima chuckled and replied, "You were already fast asleep when I got back. I didn't want to wake you, so I just laid down beside you.
Then later, you started kicking off your blanket. I didn't want you to catch a cold, so I held you while we slept. Feeling tired?"
Tsunade beamed. "You're the best, Arima-nii. I slept so well. Not tired at all."
She sniffed him curiously. "Why do you smell so nice?"
Arima honestly didn't know.
So he said mysteriously, "When I was little, I dreamed of the Sage of Six Paths. He told me I'd be holding little Tsunade a lot in the future, so I couldn't smell bad."
Tsunade blinked in awe. She always believed everything Arima said, and since he claimed her grandma knew about it, she believed it even more.
Seeing her amazed expression, Arima couldn't help but grin. He didn't plan to explain further.
After all, he believed it himself, especially since he had a "do a good deed a day" system in his head.
Just then, the door opened. Arima's mother entered, smiling as she saw the two children still playing on the bed.
"Come on, you two, time to get up. You're going to be late."
The two scrambled to their feet, washed up, ate in a hurry, and rushed out toward the Academy.
As they neared the school and saw how late it was, Arima suddenly stopped and leaned in, whispering mysteriously, "Tsunade, close your eyes and count to ten. I'm going to show you a magic trick."
Of course, she believed him. Arima-nii never lied.
Arima scooped her up in his arms. "Hold on tight around my neck."
She nodded, hugging him closely, and started counting aloud.
Though still not entirely fluent with the Flying Thunder God, Arima was confident he could manage it with enough prep time, and he wanted to make a statement with their arrival.
As she counted to eight, Tsunade felt him hug her tightly, then let go. Though curious, she kept her eyes shut and finished counting.
When she opened her eyes, she found herself standing on the stage at the Academy's opening ceremony.
Surrounded by hundreds of children, she blushed furiously and buried her face in Arima's chest.
At that moment, Arima appeared on the platform with a swish, holding Tsunade in his arms. A second later, the Second Hokage materialized as well, having used the same technique.
The watching crowd couldn't help but murmur, "Like granduncle, like grandson. Even their entrances are in sync."
Feeling Arima and Tsunade appear behind him using the Flying Thunder God, Tobirama smiled, satisfied.
And just like that, Arima began his life as vice-principal and head instructor of the Ninja Academy, in the most high-profile way possible.