Riyo in Gachiakuta: Complete Profile Guide

A Hidden Past (Spoilers Ahead)

Riyo's got a hidden past: she used to be an assassin. The team's keeping this fact under wraps. Enjin's the only one who knows, and he might've chosen to keep it that way, knowing that if others found out, their view of Riyo could change and the team's atmosphere might suffer.

When Enjin brought her into the Cleaners, he gave her one important rule: she must never take another life. This restriction wasn't just a condition, it was also a sign of trust. It showed that he thought Riyo could turn the skills she used to kill into something good, allowing her to start a new chapter in her life.

Source : Anime Gachiakuta Official