unlikeable character has tons of character development

unlikeable character has tons of character development and becomes likeable as the drama progresses

Takane to Hana - a teenage girl takes her older sister's place in a marriage meeting with the heir to a large business (sister has a boyfriend). Nothing is expected to come of it, but she takes offence at the heir's smug attitude and gives him a piece of her mind whereas all other future mates have fawned over him. He is supposed to be 10 years older. The premise deals with the age difference; however, the ML was played by a younger actor who looked like a teen himself.