Arakawa Under the Bridge

Original title: 荒川アンダー ザ ブリッジ THE MOVIE

Riku, the heir to a corporate conglomerate, is determined to go through life never owing anything to anyone on principle. However, one day he nearly drowns in a river and is saved by a homeless girl named Nino. To repay his debt, he begins living together with her on the banks of the river as her lover.