Koihime + Musou: Doki! Shoujo Darake no Sangokushi Engi

Timeslip!? Kazuto went out to catch a thief that had broken into the local Chinese history museum late one night. But after a sudden confrontation with the thief, he finds himself absorbed in a white light only to awaken in a wasteland. What’s happened!? He is surrounded by three bandits. They try and steal his school uniform, but when he refuses to let them take it they attack. Just when he thinks he is about to be killed, a girl appears in front of him. She attacks the bandits with a spear of some kind and forces them to flee. “My name is Kan’u, My Lord. As the Messenger from Heaven please stand with me to help bring peace to this country at war.”

Source: TheGamesDB