Rei is OTOKEI's bassist, backing vocalist, and producer, responsible for making Mari's mad musical experiments actually work and giving the band's arrangements texture. Their playing is restrained and effects-heavy. They first became interested in music through messing around with audio software and old equipment, eventually picking up the bass as another way to experiment with sound. Their low, calm backing vocals provide a nice contrast to Tsubaki's higher, more expressive voice.

Rei is kind of blunt, but also easily embarassed. They have a genuinely caring side, but frequently miss subtle social cues and jokes. They love dressing up and have remarkably expensive taste in clothes and perfume.

Raised by their father, who runs an electronics repair workshop, Rei developed a love for tinkering with technology and figuring out how things work. Their mother died from cancer while they were still young, and Rei struggled with depression and dysphoria throughout their adolescence despite their father's increasingly desperate attempts to help them through their shared grief.

Rei learns quickly by watching and remembers obscure trivia, but their attention is painfully selective. They can spend hours producing, tinkering, modifying their equipment, or fixing something and completely forget rehearsal. Their other weakness is cute mascot merchandise, particularly gachapon machines, which they will waste ridiculous amounts of money on just to get their favorite one.

Rei is now on HRT, which has noticeably lowered their voice over time. Their older recordings have a much higher, more feminine voice, making the difference especially obvious to longtime listeners.