Omamori Himari

On the day of Yuto's 16th birthday, he and his childhood friend Rinko meet a mysterious katana-wielding girl on their way to school. The girl starts to lick Yuto face much to Rinko's shock, forcing her to drag him away. At school during a heated arguement on the rooftop, Yuto and Rinko are attacked by Taizo who is possessed by a demon spirit until the mysterious girl from earlier excorcises it and kills it. Later that evening, Yuto is met once again by the mysterious girl who introduces herself as the cat spirit Himari, and explains he is being targeted by ayakashi who are out to kill him and that she will protect him from them. However, Rinko appears unexpectedly and causes a ruckus after seeing them together. The following day, Himari transfers to Yuto and Rinko's school. The night before, Himari reveals that Yuto's family is one of the twelve Demon Slayer families that killed ayakashi for hundreds of years, and that one of her ancestors was spared by Yuto's ancestor that led to a vow for her kind to forever serve them. Refusing to accept this fact, Rinko challenges Himari to a sports battle for Yuto's custody, only for her to lose in all of them. After being told by Himari that she lacks the strength to protect Yuto, Rinko insults her by calling her a monster. After school, Yuto reconciles with Himari on the rooftoop, who asks if it is okay to have an ayakashi like her around him. Yuto, understanding that she is only concerned about his well-being like his grandparents were, allows her to perform her duty. The next morning, Rinko comes to apologize to Yuto only to see Himari in his bed to her discomfort and it turns into yet another ruckus. Meanwhile, the ayakashi plan their move to kill Yuto when a mizuchi named Shizuki appears, claiming she will kill him herself.

Yuto, Himari, and Rinko are invited by their class representative for a trip to the beach as a welcoming gift for Himari. While walking home from school, Yuto reluctantly agrees to take Himari swimsuit shopping, in which Himari goes ahead of him. While calling Rinko, rain starts to fall, forcing Yuto to hide under a bridge where Shizuku warns she will kill him if he goes on with his Demon Slayer heritage and vanishes with the rain clearing up. While at the beach, it is revealed that Himari has a fear of water, in which Rinko throws her an inflatable whale toy to float on. While the others are having fun, Himari, far from the shore, gets a startling visit from Yuto when a giant wave appears from behind and crashes onto them, in which both of them survive but are dragged down into the ocean by a set of tentacles. When Yuto comes to in a cave, he meets Shizuku, who warns him that his awakening as a Demon Slayer will destroy the balance between humans and ayakashi. Just when she is about to kill him, Himari intervenes but another mizuchi appears from behind and grabs her while Shizuku conjures up a whirlpool to drown her. Yuto quickly jumps in the whirlpool and manages to rescue her but drowns after. Himari saves him by stabbing her leg with one of Shizuku's ice spikes, causing the whirlpool to disintegrate from her blood and allowing her to kill the mizuchi inside of it. Himari tells Yuto to run while she holds Shizuku off despite her injury but Yuto refuses, telling her not to sacrifice herself for his sake. Deducing there is something wrong with them, Shizuku withdraws from the battle not before telling them that she will kill them next time and disappears.