Akane Inui

Akane Inui is Seishu Inui's older sister.

[Spoiler] Akane was a childhood crush of Kokonoi. While walking her to her home, Koko promised Akane that he would protect her, but not long after, her household was set aflame. He ran through the fire to save her, but mistakingly rescued her younger brother Seishu instead. This accident led her to be severely burned throughout her body. No longer after, she, unfortunately, passed away. [/Spoiler]

(Source: Tokyo Revengers Wiki)