Kon Rak Game Pa Ya Bat

Kompai is a high-spirited and mischievous five-year-old girl living happily with her parents and grandmother. Her life changes when her three-year-old cousin, Rosarin, comes to live with them after losing her parents. Initially, Kompai is a difficult older sister, even going so far as to push Rosarin into the water. Though Kompai is severely scolded for the incident, Rosarin defends her, prompting Kompai to transform into a protective and loving sister.
Tragedy soon strikes Kompai’s family as well; both of her parents pass away, followed shortly by her grandmother. Now orphaned, Kompai and Rosarin are taken in by Ing-on, the mother of Kompai’s close friend, Kanliu. This shared upbringing cements the bond between Kompai and Kanliu as best friends.
During their university years, Kompai meets Wut, a close friend who harbors secret feelings for her. Lacking the courage to confess, he uses Rosarin as a "bridge" to stay close to Kompai. When he realizes Kompai has no romantic interest in him, he gives up and gets engaged to Rosarin before leaving to study abroad, promising to return and marry her.
While abroad, Rosarin’s friend Thita also goes to study in the same place. Rosarin asks Wut to look after Thita, never imagining she would be betrayed. The two begin a secret affair, and Wut eventually sends a letter to break off the engagement. Devastated and heartbroken, Rosarin withers away and passes regardless. Consumed by grief and rage, Kompai and Kanliu vow to make the pair suffer just as much as Rosarin did.