A girl named Iroha, who lived with her mother, finds her life changing when her mother remarries and brings in Rika, an older sister figure close in age. Having grown up with her father, Rika has a straightforward, no-nonsense personality, and Iroha quickly warms up to her. Iroha soon learns that Rika had been a lesbian since her own days as a schoolgirl. Secretly attracted to Iroha, Rika eventually confesses her feelings. Their relationship begins to shift into something entirely new and intimate.