Sangoku Rensenki: Otome no Heihou!

Yamada Hana, a high school girl, woke up and found herself in a strange land after being enveloped by a bright light that came out from a mysterious book. There, Hana met a young man named Gentoku, and ended up staying with him and his army as "Koumei's disciple."

(Source: Iskultrip Scans)