Yori and his twin sister, Iku, used to be inseparable, but he's been withdrawing from her lately, avoiding her altogether. Iku is puzzled by his shift in behavior since she has no idea Yori harbors romantic feelings for her. Yori's unrequited love is all-consuming; it keeps him awake at night, sharing a room with Iku, who sleeps on the bunk bed above him. Attempting to rid himself of his forbidden desire, Yori begins sleeping with Iku's best friend and applies to a boarding school elsewhere. However, Yori's emotions can't stay buried for long, and he eventually confesses his feelings to Iku when she begins discussing her boyfriend and their dates. Despite Iku's affection for her brother and a desire to stay close, Yori wishes for more than just a sibling bond and wants to explore a romantic relationship with her.