Ryuurouden

Middle schoolers, Shiro and Masumi, encountered a mysterious dragon that brought them back to the time of the Three Kingdoms; situated in ancient China. As soon as they arrived, they were rescued by the Han Kingdom. Not long after these events, Masumi was kidnapped and Shiro barely escaped death... Soon the story gets more complicated as they are stuck in the past.
(SourceL JanKenPon)