Himari

Omamori Himari (おまもりひまり?, lit. "Protective Charm Himari") is a Japanese manga series written by Matra Milan, about a boy whose life is turned around on his 16th birthday when a mysterious girl appears as his bodyguard against the demons that are now trying to kill him. It was first serialized in Fujimi Shobo's manga magazine, Monthly Dragon Age. The manga is licensed in North America by Yen Press and in Taiwan by one of Kadokawa Shoten's subsidiary company, Kadokawa Media.

In the fifth tankōbon of Omamori Himari, the author announced that the manga will be adapted into an animated series by Zexcs.

Seven years ago, Amakawa Yuuto's parents died leaving him living alone without a single relative. Ever since then, his childhood friend, Kuzaki Rinko, has woken him up, cooked for him and generally taken care of him. The only thing he has from any relative is a mysterious charm, a red ball, given to him by his grandparents as a good luck charm (an omamori).

From the day of his 16th birthday, his charm is said to not be able to protect him from evil spirits anymore, and Himari appears in Yuuto's life. Himari is a cat spirit-samurai girl and demon huntress who, aside from wanting to copulate with him madly, swears to protect Yuuto. There is only one small problem: Yuuto has a severe allergic reaction to cats.

Yūto is the only living descendant of the Amakawa Clan, one of 12 ancient demon-slayer families. Yūto's parents died in a car accident when he was young, causing him to fall into a state of depression. It was only through the care and help of his childhood friend, Rinko, that brought him out of his depression. All his life, Yūto possessed a charm that was said to ward off evil spirits, but that the charm would stop working on his 16th birthday. On the day of his 16th birthday, Yūto meets Himari, a katana-wielding girl at his school. Himari is actually a cat spirit and descendant of a clan of spirit that have served the Amakawa for many generations, and it is her duty to now protect Yūto. This is complicated however by the fact that Yūto has an allergy to cats that cause his eyes to water and his nose to run. Yūto's life becomes more complicated when he discovers that he can wield the "Light Ferry", the Amakawa Clan's ancient demon-slaying power that is both feared by demons and spirits and coveted by members of the other demon-slaying families. Initially unable to wield this great power voluntarily, Yūto has since learned to exert some minor control over his power.

Source: Wikipedia