A young man is drawn by his eccentric new girlfriend into her home, a village of eccentrics who live under a bridge on the Arakawa River.

Kou Ichinomiya is the son of a wealthy businessman who holds a firm belief in his elite status. As such, he is determined to avoid becoming indebted to anyone; but one day, after a run-in with some mischievous kids on Arakawa Bridge, he ends up falling into the river running underneath. Luckily for him, a passerby is there to save him-but now, he owes his life to this stranger. Angered by this, Kou insists on paying her back, but this may just be the worst deal the arrogant businessman has ever made. The stranger-a stoic, tracksuit-wearing homeless girl known only as Nino-lives in a cardboard box under the bridge and wants only one thing: to fall in love. Asking Kou to be her boyfriend, he has no choice but to accept, forcing him to move out of his comfortable home and start a new life under the bridge.—MAL Rewrite

Ko Ichinomiya's family motto is "Never be indebted to anyone," but after losing his pants and falling into the Arakawa River, he quickly finds himself in debt to his savior, the cutely insane Nino (who happens to live under the bridge). To repay her, he vows to help her with her desire to "experience love." Along the way he'll meet the river's other residents, including a hot-blooded kappa, a Sister in drag, and a literal rock star. Sorry, Ko-when you fell into that river, I guess you really got in over your head.—Crunchyroll