A cavity becomes a character, and somehow that's not the joke, it's the whole point. Caries lives rent-free in Ame's mouth and calls her "Mama," which means every tooth decay moment is also a relationship, every sweet snack a small betrayal of something that depends on her. The comedy isn't about gross-out humor; it's about a kid and her parasite learning to coexist in the most mundane, intimate space possible.

Ame is a young girl with a big love of sweets, and living inside her mouth is a cavity named Caries. Caries calls Ame "Mama" and does whatever she pleases, treating Ame's teeth like furniture and sometimes even seizing control of her body. Ame ends up constantly at the mercy of her unruly tenant. The pair make an odd sort of mother and daughter, and their messy everyday life together is played for slapstick laughs in this 24-episode run of short comedy episodes.