|Japanese VA||Satou Azusa|
|English VA||Kendall McCellan|
While in high school, Aiko is a plain yet beautiful girl with middle-long black hair that is kept in a ponytail, her hair is parted in the middle with some strands falling besides her face in the front, black eyes and ordinary glasses.
Her clothes is the school's uniform: a dark blue blazer, white shirt, a short skirt and a tie.
Aiko only appeared in the story in Ryōta Sakamoto's flashback in high school. There, she was the object of Sakamoto's affection. Even though he was in love with her, he didn't have the courage to confess to her. After Sakamoto told Nobutaka Oda about his feelings for Aiko, Oda insulted him being too naive and being an idiot. Oda explains that if Sakamoto is too passive, Aiko would be with someone else. The next day of class, Oda had sex with Aiko after she had confessed to Oda. When her friends and Oda's girlfriend found out about it, she burst into tears in guilt and Sakamoto attacked Oda, partially because of Aiko.
Aiko has confessed her feelings for Oda. The two had sex. She feels guilty when her friends and Oda's girlfriend had found out about their affair.
- The name Aiko means "love, affection" (愛) (ai) and "child" (子) (ko).
- Aiko's surname Serizawa means "celery" (芹) (seri) and "swamp" (沢) (sawa/zawa).
- Btooom! manga, chapter 42, page 31