Age: 19
Height: 156cm
Favorite Color: Pink

Sumi is one of the main deuteragonists of Kanojo, Okarishimasu. She is a first-year college student who works as a rental girlfriend for the Diamond app. She's shown to be extremely shy and timid but slowly starts to open up the more time she spends with Kazuya. Despite her shyness, Sumi is also shown to be a very determined individual. She's realized that her shyness has become an obstacle in her day-to-day life, so to overcome it she started working as a rental girlfriend.

Chizuru serves as her friend and mentor within the agency.