Sora wa Akai Kawa no Hotori

A seemingly ordinary modern day teenager, Yuri, is suddenly whisked away to the Hittite empire in ancient Anatolia, where an ambitious queen wants the girl for a blood sacrifice in order to murder all heirs but her son, thus seizing control of the throne. Luckily, the timely intervention of Prince Kail saves Yuri from the queen's grasp. Kail promises to send Yuri back to her home, but the queen's persistent schemes to kill them both, plus their growing feelings for each other, keep those plans delayed.

(Source: Wikipedia)

Included one-shot:
Volume 28: Orontes Renka