Transmigration

"Aizen, wait for me! In the combat class next month, my eldest brother will definitely avenge me!"

The Land of Fire, Konohagakure, the gate of the ninja academy...

A boy, about eight or nine years old, his face bruised and swollen, roared viciously at another boy in front of him, his voice tinged with tears.

After speaking, he turned around and ran away, as if afraid that his words would provoke retaliation from the person he addressed.

Looking at the boy who had fled without a trace, the young man he had spoken to did not respond, instead appearing dazed and oblivious.

"Oh, this guy, you've scared him senseless!"

"No, I've heard that the eldest brother of the Sarutobi clan is the famous Senju Nawaki. This guy Aizen will be embarrassed in next month's combat class."

"Hmph," scoffed another. "A measly civilian dares to defy a ninja clan? He had it coming. Serves him right for being disrespectful!"

"Yes, let him understand that in all of Konoha, only we nobles are the real ninjas!"

It was the closing time of the ninja academy, and an endless stream of students were heading home.

After witnessing the earlier altercation, waves of regretful sighs and ridicule were directed at the young man.

Listening to the surrounding discussions, the boy called Aizen still did not respond. At this time, only the famous three questions of life echoed in his mind...

Who am I, where am I, what am I doing?

I, Aizen, was originally a scholar living on Earth.

Apart from not possessing the earth-shattering strength of Aizen Sōsuke, the famous villain from the world of Shinigami, I was by no means inferior to him in terms of mental ability.

When I was only fifteen years old, I entered the junior class of an esteemed university. At eighteen, I obtained a doctorate in biology from the same institution. At twenty-two, I joined a top biological research institute and engaged in confidential research work.

I am a genius with grand ideas and vision.

I sought to change the fragile nature of human life, to use bioengineering technology to grant the human body longer lifespans, and even bestow extraordinary abilities!

In the end, I was almost there. 

Through frantic, all-consuming experiments, I created a human cell-based transformation being.

Not only did it possess the regenerative abilities of lizards to regrow severed limbs, but also the bioelectric discharge capabilities of electric eels.

Seeing the realization of my long-held dream, I trembled with excitement, and immediately set about undergoing my own biomodification surgery. 

And it's true that biomodification is an extremely complex and rigorous science.

Every life is uniquely constructed. Just as doctors prescribe different medications, dosages, and even different medicines for people with the same disease according to each person's individual conditions. 

I am a cautious person.

Initially, I tested the fusion of my own cells with the modified cells, and later cloned my own body, conducting over ten bioengineering experiments... 

The results were all great successes.

Then, with utmost confidence, I proceeded with reconstructive surgery on myself. 

Alas, due to cell rejection, I... perished.

A generation of genius lost! Woe is me!

"Me? It seems like I'm dead...But isn't this death? And what is this place all around?" I looked at my small hands and feet, then at the unfamiliar environment surrounding me, my expression one of utter confusion.

"Ah, it hurts, it hurts!" 

Suddenly, a sharp, needle-like pain swept through my mind, and at the same time, a flood of unfamiliar memories!

This caused my body to involuntarily lean against a nearby pole, as I covered my head with my hands, my face contorted in agony.

After a long time, when the pain subsided, a memory named Konoha Aizen appeared in my mind. 

Moreover, this other entity also shared my name and surname, also called Aizen.

At the same time, I learned the fact that I had traveled to the world of the ninjas.

As is so often the case, the protagonist's parents had high-risk occupations... 

The original owner's parents died on a mission, fulfilling the basic prerequisite of parental sacrifice.

And the original owner himself excelled at the ninja academy. 

Though not comparable to top talents such as the highly anticipated Namikaze Minato and Senju Nawaki, nor to the prestigious bloodline clans like the Hyuga, Aburame, Inuzuka, and Ino-Shika-Cho, his results still placed him in the top ten of his grade, second only to the upper echelons.

To put it mildly, he was a prodigy. 

Not only that, but the original owner was sincere and gentle toward others on a daily basis, always helping fellow students in need within his capabilities. As such, he had an excellent reputation among many students, especially those from civilian backgrounds. 

Of course, this wasn't an entirely good thing.

The Sarutobi clan held a reputation for bullying civilian students at the academy. They lorded their clan name and impressive skills over their weaker classmates.

The original Aizen just happened to witness Sarutobi Funari picking on a classmate, Kitagawa Shuji, a close friend of his. Fueled by righteous anger, the original Aizen intervened and taught Sarutobi Funari a lesson.

Of course, while his actions stemmed from loyalty, they also planted the seeds of future trouble.

This revelation left Aizen speechless. Hadn't the original Aizen been foolish? Offending the Sarutobi clan for a friend and unwittingly provoking a prodigy like Senju Nawaki.

Memories of the original Aizen suggested Senju Nawaki might be a bit of a hothead, similar to Uzumaki Naruto. But here's the kicker: Nawaki later became Orochimaru's apprentice! Aizen found it hard to believe someone with Naruto's personality would appeal to Orochimaru.

"This is a real mess! The original Aizen is nothing like his namesake from Bleach. Here, lacking both IQ and talent seems to be a recipe for disaster. In this world of Naruto, where bloodlines hold immense power, isn't this a setup for failure?" Aizen thought with growing anxiety.

Suddenly, a voice echoed in his mind:

[Ding! Soul transmigration and merging was successful. Activating Villain System!]