Gunjou Senki

Gunjou Senki (グンジョーセンキ, Gunjou Senki) is a manga written and illustrated by Masaki Kasahara. It was serialized in Young Jump.

Plot
High-schooler Nishino Aoi is a history nut who's in the archery class at his school. Due to his skill in archery, he sometimes thinks that he's more suited to the Sengoku period of Japan. If he lived then, he imagines he might even have a girl like his clubmate Seno-san as his wife. As it is, Seno-san is his friend and the girlfriend of his childhood friend Kouta.

When a mysterious fog covers the school, Aoi gets his chance to experience the Sengoku period first hand. The entire school is transported to a time period that Aoi pinpoints as somewhere between 1576-1582, near to Azuchi Castle. However, things are not as bright as he might have imagined. Armed men accompanying the historical figure Hachisuka Koroku attack the school, brutally murdering teachers and students. Will Aoi and his friends be able to survive this deadly era?