Yakuza Girl – Blade Shikake no Hanayome

Yakuza Girl – Blade Shikake no Hanayome (ヤクザガール 〜ブレイド仕掛けの花嫁〜, lit. "Yakuza Girl – The Blade Wielding Bride") is a manga written by Masaki Motonaga and drawn by Yu-Go Okuma. It began in February 2008.

Plot
Senguu Fumihiro is a young boy that made a promise to his dying grandmother to find a good wife for himself. With this intention he enrolls in a prestigious school but on the first day his world turns upside down when all the students begin to kill each other and one of them even turns into a monster. He is saved by a girl named "Akari" sent by one of the factions that rule the school to protect him.