Origins

On the first anniversary of the First Hokage's death, Senju Katsuro was born. Despite his birth date being an ill omen, Mito Uzumaki, wife to Senju Hashirama, took notice of the new leaf sprouting.

As a child, Katsuro was praised as the genius of the Senju clan throughout the village, and when admitted to the academy at 4, this was only amplified. With both his parents, Senju Raito and Senju Hana, being Shinobi, he could perform the 3 basic Jutsu of the academy with ease while also being proficient in Taijutsu and even Kenjutsu. He would consistently overcome the Uchiha's genius, Fugaku, during sparring, and even match him with their specialities in kunai and shurikenjutsu. Naturally, this bred resentment in Fugaku, who saw the Senju - and Despite the constant requests to spar, a sense of camaraderie was bred between the two over time built upon Katsuro's nature.

But even during times of peace, the Shinobi world dealt its cruel cards. The Jonin, Senju Raito and Chunin, Senju Hana, had been on a mission in Amegakure. It seemed like everything had been going smoothly - in fact, the Shinobi team had completed their mission, and were on the way back to Konoha - but they never made it. They had been ambushed by enemy Shinobi right at the border of the 2 lands, badly outnumbered against a squad of 3 Jonin and 5 Chunin. They fought valiantly, as expected, dying doing their duty while bringing down some of their foes with them. The village hailed them as heroes. But what about the child they had left behind? What about him?

He had lost both his parents in a place he didn't know, doing a mission he didn't understand. At first, the small child didn't understand.

"Where are my parents? I want to see my mum and dad!" he demanded the Shinobi that had come to his home to deliver the news, and then later to the Third Hokage. To him, this was just another work trip that his parents had gone on, and they were just later home than normal. It wasn't until he was brought under the care of Uzumaki Mito that he truly realised what had happened.

They weren't coming back from this mission. They weren't coming back. Ever.

His life, which previously seemed bright - perfect, even, was clouded in darkness and eventually a cold fury toward himself, unnatural for a child of his age. Everything seemed to move by in a blur. He barely remembered the funeral - just people wearing black clothes, offering their condolences. Heartful yes, but useless all the same. It seemed like the world itself mourned their loss, with the sky filled with dark clouds pouring rain, but for what? None of this is going to bring them back. Not now, not ever. 

The cold fury returned now, greater than ever.

Katsuro made a vow to himself and his deceased parents, that he would not be as powerless as he was now, that he would protect what he cared about.

The attempts of his classmates and Fugaku to console him proved futile; he became a boy obsessed with strength. Any spare time was spent on tree walking to water walking to enhance his chakra control, among other exercises, to leash his huge amount of chakra as a result of not only being a Senju, but also having unlocked those memories. This combination of spiritual energy (yin) and physical energy (yang) led to a chakra amount equaling a Kage at his young age, which would grow exponentially. Mito clearly sensed the guilt and distress lying underneath his sombre but determined attitude took another path. She began to teach him Fuinjutsu, the speciality of the Uzumaki clan, directing his fire toward it while telling him stories of Lord First.

"Why are you training so hard?"

Katsuro turned from the ink and paper, looking up blankly at Mito, who for all intents and purposes was his grandmother. 

"To make sure those I care about never get hurt again."

Mito chuckled lightly, "So in the process of protecting your family and friends, you neglect them and don't spend time with them?" Seeing Katsuro's confused look she continued. "Merely in the second year of the academy, you train so hard, day and night, and can probably already beat most Chunin, but you've lost the bright personality that used to care for the very people you wanted to protect."

Katsuro's mouth opened, but no words came out. 

"While it's good to want to grow stronger, live your life, Katsuro. Even Hashirama, who they called the God of Shinobi, made sure to spend time with his family because, ultimately, they are the reason you want to get stronger."

"Alright Obaa-san. I'll try."

Mito smiled, "That's all I ask, my boy."

Katsuro continued to train like a devil possessed but glimpses of his old playful and cheery personality slowly returned. Granny Mito was right - his parents hadn't sacrificed their lives just for him not to enjoy his own. That being said, it was easier said than done. I'll be happy, he thought to himself. I'll be happy, after I've done what I need to do.

AN: Edit: Removed the glimpses/dreams Katsuro was having alluding to remembering the series; the story will no longer go in that direction after some feedback and my own decision. Sorry for any confusion down the line! Thanks!