Sasami-san@Ganbaranai centers on Sasami Tsukuyomi, a first-year high schooler whose life has narrowed into that of a hikikomori, one of the socially withdrawn people in Japan who refuse to leave home for weeks or even months. She is still trying to pass school from inside her room, relying on her older brother Kamiomi—who also happens to teach at the school she is supposed to attend—and on a "Brother Surveillance Tool" that lets her watch the outside world through her computer. In theory, that system could help Sasami readjust to dealing with other people again.
Instead, it mostly feeds her fixation on Kamiomi's daily life, especially his encounters with the three deeply strange Yagami sisters: Tsurugi, Kagami, and Tama. The sisters seem to have had their ages reversed, and each shows her own kind of "interest" in Kamiomi. As Sasami keeps watching from a distance, ordinary life begins to give way to surreal disorder. Magical powers erupt without warning, the world can suddenly turn into chocolate, and the boundary between shut-in isolation and cosmic absurdity starts to collapse. Whether Sasami's life through the web is distorting her view of reality or the universe itself is spinning out of control, her secluded routine becomes entangled with something far stranger than everyday school life.