Second daughter of the Tsukishima family, in 5th grade in Part One. Through their childhood, Wakaba is constantly with Kō. She constantly talks about their future together, even giving him a schedule of suggested future birthday gifts that includes an engagement ring for her 20th birthday. She frequently kisses Kō, which annoys their mutual friend Akaishi, who has a secret crush on her. For several birthdays in a row, Wakaba gives Kō alarm clocks because he has a hard time waking up in the morning.

Her name means "young leaf".