18+ Kimi ni Somaru Monochrome

Hajime Haibara's daily life faded into monochrome as his first love disappeared. Seven years later, he is now a high school student, and a beautiful girl named Misora Rurikawa, who draws erotic manga without being noticed, appears in front of him. I can show you a 'new world,'" she says, taking him to a large-scale doujin event!

(Source: Cygames, translated)