Ever since graduating college, 23-year-old Meiko Inoue has believed in one thing: there is a demon lurking in Tokyo. This evil's presence has made her bored, aimless, and missing the excitement of her youth, leading her to contemplate what she truly seeks from life. Surprisingly enough, when Meiko proposes the idea of quitting her job to her boyfriend, Naruo Taneda, he groggily agrees.

Deeply inspired by his half-asleep words of encouragement, Meiko hastily leaves her old life behind, looking to begin anew, with Taneda soon following suit. Together, they look toward their dreams from their college days and decide to revive Rotti, Taneda's old band. As the two stand confidently alongside their old friends with instruments in hand, life throws the most unexpected curveball their way, leaving Meiko and her friends to pick up the pieces of what was shattered.

Solanin tells an intimate story about the trials and tribulations of love, loss, and grief centered around people in their twenties who often slip between the cracks of society.