Pitsawat Onlaweng

When coming back from abroad, Chang is forced by his mother to get engaged to some spoiled, bad-tempered brat. Someday, while trying to escape his fiancee during a date, Chang get hit by Beam's car. When she brings him to her home to make sure he's okay, he wakes up with a loss memory and the mind of child. Beam then nicknames him "Somchai" and decides that she will take him to the doctor in the morning. But after a good night's sleep, Chang gets his memory back. However, he lets Beam think he's still amnesiac and keeps on behaving like a kid to stay with Beam as he doesn't want to go back to his awful fiancee and starts having a crush on Beam.
(Source: Vico SDL at MDL)