"MSAC” is a rare and bizarre disease that is said to develop when feelings of affection, vindictiveness, or regret for a particular person swell up. There are a variety of symptoms, and no fixed cure has been established.

One day, one of the new part-timers at work, Io, confesses his love to Mitsuri, who is gay and has a male love interest. Io is an excellent boy with a good memory, but he has a certain aloofness that prevents him from grasping his true feelings. Although he suspects that Mitsuri is making fun of him, he gradually becomes aware of him. Mitsuri's messed up feelings overflow into a disease called “MSAC”..!