Shotaro Tokito, a university student, shares a room with his childhood friend Rin Kazama. When they were kids, the two of them went everywhere and did everything together. Shotaro was always overprotective of Rin, who always followed him around, but after they started living together, Rin's attitude became cold and he started playing around with women... Before he knew it, a gap had formed between the two of them. One day, they got into an argument after Rin brought a woman into the house without permission, and in the process, Rin hit his head and lost all memory of their relationship. The two decided to continue living together as before for the sake of his treatment, but Rin is still as attached to Shotaro as in the past... but seems to have ulterior motives...!?
「こんな顔、知らない――」

大学生の時任翔太郎は、幼馴染の風間凛とルームシェアをしている。
子供の頃はどこへ行くにも何をするにも一緒だった二人。
いつも後ろをついて回っていた凛に、過保護に接してきた翔太郎だが、同居を始めてから凛の態度は素っ気なくなり、女遊びをするように…
いつしか二人の間には溝ができてしまっていた。

ある日、凛が女性を許可なく家に連れ込んだことから口論になり、喧嘩のはずみで頭をぶつけた凛は、対人関係の記憶を全て失ってしまう。
治療のためにも、今まで通り同居生活を継続することにした二人だったが、凛は昔のように翔太郎にベッタリ懐いている…どころか、下心を抱いている様子で――!?