On his way home from school, Tatsumi sees a man collapsed near a lake. When he approaches him, Tatsumi notices something strange: the person in need of help is actually a beautiful merman named Wakasa! Because Wakasa's home has become too polluted to live in, Tatsumi graciously offers his bathtub as a refuge. With a boisterous merman as his new roommate, Tatsumi's normal life won't be returning anytime soon, not to mention Wakasa's aquatic friends—Takasu, Mikuni, and Maki—often show up uninvited, making them all quite a handful for the high school student. As he humors their curiosity for human life, Tatsumi sometimes finds himself enjoying their childish antics, but he will have to keep his cool if he intends to keep up with his daily life and newfound friendship. [Written by MAL Rewrite]

Miou Aida and Haruki Serizawa might seem like polar opposites to those around them, but as the two third-years prepare to end their high school experience, they couldn't have been been closer. While Miou is a shy and reserved member of the school art club that prefers to stay out of the limelight, Haruki is the boisterous and confident ace of the movie club, already winning awards for his directing prowess. However, after a previous chance encounter during their school entrance ceremony, they quickly become friends despite their stark differences in personality. But although their closeness might be growing, they've never become anything more than just that, much to the bewilderment of their friends. As their time in high school draws to a close, Miou and Haruki, along with their friends in the art and movie clubs, have just one year left to face their hidden feelings and the daunting task of deciding their future careers. The two might always be only an arm's reach away, but as Haruki chases his dream of becoming a professional movie director and Miou struggles with choosing a path for herself, they'll learn just how hard it is to get past those last 10 centimeters. [Written by MAL Rewrite]

Maeda has just moved into his new apartment to live by himself. While unpacking, a cute middle school student named Chie Satonaka suddenly appears in his room. She introduces herself as his new landlord, which pleasantly surprises him as he has never seen a landlord so young. His excitement is boosted further when the gorgeous Reiko Shirai, who lives directly next to him, also introduces herself as his new neighbor. Ooyasan wa Shishunki! follows the everyday lives of Maeda and his newfound acquaintances, where each day presents itself as an opportunity for new events to unfold and new bonds to be forged. [Written by MAL Rewrite]

The anime will feature an original story from the game on which it is based.