If that were all, it wouldn't have caused such a drastic change in Sora, who had already grown used to life with Tsunade.
The real turning point came in the third month after she adopted him.
For some unknown reason, Tsunade actually developed a ninjutsu that allowed a virgin woman to gain the nursing ability of someone who had given birth.
And she cast it on herself.
From that day on, Sora no longer drank formula. Shizune didn't have to run through the streets carrying cans of milk powder anymore. Tsunade fed him personally.
If Sora were an ordinary baby, this would have been nothing.
But beneath that infant body was a mind as sharp as an adult's.
So every time, Sora blushed.
"Lady Tsunade, you're going to corrupt the child like this," Shizune muttered from the side.
She was also curious why Tsunade would go so far as to create such a ninjutsu.
When she privately asked Tsunade about it, the answer made her want to slam her head into a wall.
"No choice. This kid eats too much. If I keep buying formula, I'll go broke. This way, a small investment gives ten thousandfold returns. Not only do I save money, I get more funds to gamble!"
That was Tsunade's explanation.
Neither Shizune nor Sora believed a word of it.
"Hehe." Tsunade just laughed.
This wasn't the first time Shizune had accused her of corrupting Sora.
"Mom, I want to learn ninjutsu."
Over the past few years, Sora had gained a deep understanding of this world—not just from surface-level knowledge like in comics, but from living in it.
This was a world where the strong preyed on the weak.
For ordinary people, killing on the streets was illegal.
For samurai, it was acceptable.
For ninja, it was commonplace.
Even the ninja of the Five Great Villages regularly accepted assassination missions, and no one found it strange.
Sora understood one truth clearly:
The weak had no dignity.
To live freely, one needed strength.
If Tsunade weren't one of the Sannin, if she weren't the princess of Konaha, with her beauty alone she would have been kidnapped countless times.
Yet she gambled everywhere, owed debts Sora estimated to be at least tens of billions, and still lived freely.
Why?
Because she was strong.
After careful consideration, Sora decided to learn ninjutsu from Tsunade.
Not for ambition.
But to one day repay the nurturing kindness of the woman before him.
"You won't regret it?"
The smile disappeared from Tsunade's face.
She thought of her younger brother. Wasn't it because he became a ninja that he died?
Deep down, she had wanted Sora to live as an ordinary person.
Over the years, she had truly come to regard him as her own child. Otherwise, she would never have created that ninjutsu just to personally feed him.
She had already accepted the role of mother.
"Survival of the fittest. Only the strong survive."
Sora spoke calmly.
On Earth, those words were true.
Here, without the protection of law, they were even more brutally true.
He didn't want to be powerless when misfortune struck.
He didn't want to stand helpless if Tsunade ever needed him.
"...Alright."
Tsunade's eyes flickered with hesitation.
Ten full minutes passed before she spoke again.
"But once you start, there's no turning back. When I teach you, I am not your mother. I am your teacher. You must be prepared to die."
A cold aura spread from her body.
This was no joke.
The path of a ninja was paved with blood.
Even someone as strong as Tsunade could fall with one mistake.
Better to sweat more in training than bleed in battle.
"I won't die."
Sora said each word clearly.
Inside, he added silently:
I haven't repaid your kindness. How could I die?
"Good. Come with me."
Tsunade brought Sora to a spacious forest.
Shizune followed quietly. Having grown up under Tsunade's guidance, she knew exactly how brutal Tsunade's training methods could be.
But she was prepared.
Over the years, she had grown fond of Sora as well. His arrival had changed Tsunade. The once-dispirited woman now smiled genuinely from time to time.
"Sora, listen carefully," Tsunade said seriously.
"Between ninja, there's no room for fancy tricks. Once a battle begins, it's either you die or I die. If you ever dare to hold back in a real fight, I'll be the first to deal with you."
Her voice was cold and absolute.
"A ninja's abilities are divided into three main categories: ninjutsu, gengutsu, and taijutsu. Beyond those, there are special abilities like Bloodline Limit, Forbidden Jutsu, and Secret Techniques. Those are still far from you. Just remember they exist.
No matter which path you take—whether balanced or specialized—you must have a strong body. Your current body is too weak. It can't endure battle, nor even daily training.
The body and Chakra complement each other. Chakra is formed from spiritual energy and physical energy. If your body is weak, you won't be able to refine much Chakra. You might not even be able to control it properly."
Her explanation was concise and direct, every sentence striking the core.
Sora realized the importance of having a great teacher.
A genius without guidance might never become strong.
An average person, with the right teacher and effort, could surpass limits.
And Tsunade was one of the Sannin of Konaha. A veteran of war. A member of the Senju Clan.
Teaching him was effortless for her.
"Starting today, your priority is to strengthen your body as quickly as possible and learn to control it. Once you meet my standards, I'll teach you how to refine Chakra."
She finished speaking and immediately assigned tasks.
Sora was stunned.
Even though he had mentally prepared himself, he was still shocked.
Tsunade wanted a three-year-old child to:
Run five kilometers.
Do one hundred push-ups.
One hundred squats.
One hundred sit-ups.
This wasn't training.
This was attempted murder.