Wasureta Koi no Shuufuku Hou

One day, I woke up to find that my best friend had become my lover.

Yagi Shouma, eighteen. I was supposed to be in love with Mizuki, my childhood friend, but when I woke up, there was Mizuki, who claimed to be my "boyfriend," all grown up. I am now an adult too, but it seems that I have lost seven years of memories. The adult Mizuki I don’t know is somehow sexy and unsettling, and it’s overwhelming for someone who has only just realized their first love…

(Source: ShuCream, translated)