Om! Crush on Me.

To find his long-lost mom, Ryo, a half-Thai-half Japanese, comes to Ayutthaya. During that he falls in love with Saisoi, but she is bought to be a slave wife of a lord. Not only the high royal rank he has, but also the magic. Ryo has learnt about magic for a while, he forms a group with friends to set Saisoi free from being a slave. However, his magic is not as strong as the magic of the lord. Ryo comes back again and never gives up helping the girl he loves and finds a chance to meet his mom.