Rika Furude and her group of friends live in the small mountain village of Hinamizawa; in June 1983, they welcome transfer student Keiichi Maebara into their ranks, making him the only boy in their group. After school, they have fun playing games and spending each day living their lives to the fullest. Despite this seemingly normal routine, Keiichi begins noticing strange behavior from his friends, who seem to be hiding the town's dark secrets from him. Elsewhere, a certain person watches these increasingly unsettling events unfold and remembers all the times that this, and other similar stories, have played out. Using that knowledge, this person decides to fix these broken worlds. However, when certain variables change, the individual is faced with a horrifying realization: they have no idea what to expect or how to stop the impending tragedy.

The majority of the Matsuno household is comprised of six identical siblings: self-centered leader Osomatsu, manly Karamatsu, voice of reason Choromatsu, cynical Ichimatsu, hyperactive Juushimatsu, and lovable Todomatsu. Despite each one of them being over the age of 20, they are incredibly lazy and have absolutely no motivation to get a job, choosing to live as NEETs instead. In the rare occurrence that they try to look for employment and are somehow able to land an interview, their unique personalities generally lead to their swift rejection. From trying to pick up girlfriends to finding the perfect job, the daily activities of the Matsuno brothers are never dull as they go on all sorts of crazy, and often downright bizarre, adventures. Though they desperately search for a way to improve their social standing, it won't be possible if they can't survive the various challenges that come with being sextuplets!

Second season of Osomatsu-san.

Third season of Osomatsu-san.