As children, sisters Suzu and Kotone were separated due to their parents' divorce. Years later, after their father's passing, Kotone moves in with Suzu once again. One day, Kotone accidentally discovers her older sister Suzu masturbating as part of her daily routine. Learning that her sister enjoys pleasuring herself, Kotone feels a sense of excitement, and this moment becomes the turning point in their relationship. As they begin to kiss, they cross into the forbidden world of lesbian intimacy. Their bond deepens from there, evolving into a new and intense connection.