Roy Ruk Hak Liam Tawan

It is about a Thai lady name Preawdao/Seiko who just got a scholarship from Japan for her Master's degree in Economics. Preawdao's beauty impressed Takeshi, the second son of a very powerful family, Onizuka. He keeps following her from a distance but never approaches her. Finally, Ryu, Takeshi's cousin, helps him talk to her, and their relationship begins.
When Preawdao finds out that Takeshi & Ryu are members of gokudo, a powerful family, she becomes afraid and distances herself from them. Takeshi doesn’t give up and goes every day to her class to watch her from a distance. To complicate things further, Takeshi already has a fiancé his father has arranged for him from another powerful family.
When his dad and brother die from a car bomb, he becomes the Oyabun, the head of Onizuka's gang. He announces that he will not marry his fiancé until he gets revenge on those responsible for his dad and brother’s death. Aiko, his arranged fiance, is in love with Takeshi. When gangsters kidnap Preawdao, Takeshi risks his life to rescue her.
To ensure Preawdao's safety, Takeshi takes her in and announces that she is his mistress. Even more problems begin for the couple. As the head of the family, his rivals begin attacking him at his weakest point, his loved one, Preawdao. She becomes prey and a mark for all his enemies.
(Source: Sharerice.com)