Responsible Taihei has to deal with his lazy little sister, Umaru, who trashes his apartment and throws tantrums to get manga and junk food.

Taihei comes home to a complete stranger: Umaru’s public face. She’s cleaned the apartment and hidden her games to be able to invite her classmate and neighbor, Ebina, over.

Umaru’s sulky, glaring classmate, Motoba, has unexpectedly shown up at her door… while she’s wearing her hood! Is her secret out?

Umaru, aka UMR, is a force to be reckoned with in the arcade. She’s invited to participate in a fighting game championship only to bump into her school rival, Tachibana.

Summer vacation means hours at the arcade! Umaru instructs in the fine art of enjoying summer like a (lazy) pro. Later, Taihei endures another typical day at work.

Taihei and Umaru experiment with free time and personal space in their little apartment, and playing “The Game of Life” hits too close to home for them all.