Danshi da to Omotteita Osanajimi to no Shinkon Seikatsu ga Umaku Ikisugiru Ken ni Tsuite

Shuichi, a high school student, ended up marrying his childhood friend whom he previously assumed was a boy. When they met 10 years previously, his childhood buddy Yuika had evolved into a lovely girl, which originally made Shuichi somewhat nervous. But with time, he gradually became used to the intimacy of being best friends. Their story as a perfect pair with a charming hint of innocence thus begins.