Danshi da to Omotte Ita Osananajimi to no Shinkon Seikatsu ga Umaku Ikisugiru Ken Nitsuite

Shuiti, a high school student, ended up marrying his childhood friend whom he originally thought was a boy. When they reunited 10 years earlier, his childhood friend Yuika had transformed into a beautiful girl, which initially made Shuiti quite nervous. However, as time passed, he gradually grew accustomed to the sense of closeness as best friends— And thus, their love story as an ideal couple with a charming touch of innocence begins!