Isamu was born in Nagoya, Japan, to two fairly indifferent parents. He was born more out of societal expectation rather than any real desire to have a child, though that didn't mean he was hated or neglected. Isamu lived a fairly normal childhood, if a little sheltered - though it was perhaps because of this normalcy that he quickly became bored. He refused to grow complacent in this dull, passionless life, and so he sought an outlet.

Horror quickly became that outlet. Isamu was completely fascinated by the morbid imagery, the discomfort that he'd never experienced before, all the visceral feelings it had instilled him with. From the moment he had picked up his first horror novel, he had fallen in love. There were many things in it he couldn't quite understand, given his young age and limited life experience, but that only drove him to learn more. He became utterly absorbed into the world of horror, much to the disapproval of his parents, and had even began to try and write stories of his own. His new interests had made him quite the odd one out at his school, but he didn't mind.

When 10 year old Isamu wrote a collection of short horror stories for an online contest, he was immediately met with critical acclaim. The vivid and disturbing imagery invoked within his work and the thoughtprovoking themes were widely praised - even more so when people learned his age. The world had a young prodigy on their hands, and suddenly, all eyes were on him. It was also around this time that his little sister, Momo Itou, was born.

When Isamu looked upon his newborn sister for the first time, he suddenly felt conflicted. He had a break into the world he'd been fascinated by for years, but he now found himself fascinated by the innocence before him. He could leave if he wanted to, he could take on one of the many apprenticeships he had been offered in the wake of his success, but he found himself unable to abandon Momo. That girl who knew nothing of the world was his last link to normalcy and innocence, and he found himself hesitant to abandon it. Isamu continued to write on his own, honing his craft and publishing various short stories over the years, but had no intention of leaving his family's side.

When Momo was 4, and Isamu 14, tragedy stuck, and their parents unfortunately died in a car accident. This incident shook the two children deeply, and resulted in their grandparents taking them in. The days that followed were difficult and hard to navigate for someone like him, who had been living so comfortably for so long. On top of that, he was worried that the situation could turn once again, and that their grandparents could also disappear within an instant. It was with this that Isamu resolved to delve fully into the world he had been tiptoeing his way into. He turned his new raging emotions into his greatest masterpiece yet - a novel that would serve as his formal debut into the world that he had been reaching towards since he was a child.

The novel was a complete hit, bringing Isamu great relief. Not only did he now have a stable income to support his family, but he also had an outlet for all of his feelings. "Art should disturb the comfortable, and comfort the disturbed" - those words were something Isamu didn't fully understand until the moment he became the latter, and were now something he resolved to live by to the fullest. 

He continued to write more novels from that point onward until, a few years in, he was invited to Hope's Peak Academy. Isamu initially rejected the invitation, resistant to the idea of leaving Momo behind just so he could chase some prestigious title. However, Hope's Peak amended the rules and made an exception just for him, admitting Momo into Hope's Peak Elementary and allowing her to stay with Isamu in the dormitories. It was only then that Isamu accepted - his two worlds, at last, colliding into one.