It gets under your shell fast. The title isn't a cute riddle, it's the whole thesis: a turtle's shell is fused to its skeleton, so what looks like armor is just Kameda's own ribs, and cracking it open means cracking himself open. That's the trick this thing pulls in a single sitting. A high school full of animal-humans could have been a gag premise, but the clique hierarchy lands like real teenage social death, and Kameda sits at the bottom of it doing nothing about it until one chance moment makes doing nothing impossible. The animation is the reason people who find this won't shut up about it, hand-made in a way big studio work has sanded off. It's slept on because nobody handed it a marketing budget. Watch it, then go tell someone.

Kameda Kamerou is a turtle-human and an ordinary second-year student at a high school full of animal-humans. He belongs to the least popular clique, lives an uneventful school life and keeps his true feelings tucked behind his ribs. When word gets around that his best friend Kaerugawa Erutaka has helped others, a high-ranking group takes notice. That group includes the school's star, Raionji Raiou, who wants to become student council president. Kaerugawa suddenly joins them, and Kameda is left wrestling with jealousy and a sense of inferiority. A chance occurrence one day leads him to open up and face things directly, and on the day of the student council election, a clash of bones gets underway. This slice-of-life film is about conflict, friendship and growing up.