Rito Yuuki is a 16-year-old high school student who's had a crush on classmate Haruna Sairenji since junior high, but hasn't mustered the courage to confess. His situation gets complicated when Lala Satalin Deviluke, the crown princess of an alien empire, crash-lands into his life. Lala has run away from her home to avoid a forced marriage and unexpectedly asks Rito to marry her instead. This sets off a chain of events filled with romantic misadventures, slapstick humor, and unexpected romantic entanglements.