Mukashi no Otoko Tomodachi to Doukyo wo Hajimetara, Jitsu wa Bishoujo Datta: Kyori-kan ga Ano Koro no Mama de Chikasugiru

"Kei-chan, see you tomorrow!" — That promise was never fulfilled, and young Kirishima Keisuke was separated from his only close male friend, Maa-chan. Then, ten years later, the person who arrived due to their parents' remarriage was none other than Maa-chan—now Masaki—who had grown into a charming and outgoing beautiful girl!

While Keisuke, who had always mistaken her for a boy, is confused, Masaki begins interacting with him even more closely than before, as though they were siblings. Playing games together, eating meals together... and even trying to bathe together!?

As they live together, the two feel a sense of comfort, as if the ten-year gap had never existed. Yet, both their hearts and bodies have grown, and living under the same roof makes them unavoidably aware of each other...!?