She is extremely introverted and rarely speaks, often communicating through gestures or facial expressions. She decided to work as a rental girlfriend specifically to try and overcome her social anxiety. Sumi developed genuine romantic feelings for Kazuya, admiring his kindness and the way he tries so hard for Chizuru. Sumi is completely selfless. She recognizes that Kazuya loves Chizuru and, instead of competing, chooses to support him so that he can be happy.