Unlike his father, the Cat King, Prince Lune is shown to be much more friendly and humble towards his subjects and isn't fixated towards Haru. He is in fact unaware of his father's machinations, preferring to marry Yuki instead. As evidenced by his relationship with Yuki, a royal servant, he treats others fairly, regardless of class or affiliation.
The Cat Returns
Prince Lune is saved by Haru in her human form at the beginning of the film. After Haru rescues him, he offers to repay her and then one thing leads to another, until she is forced to marry him, no thanks to the prince’s father. Haru manages to escape, as Prince Lune is in love with Yuki, a cat maid who had befriended Haru. Additionally, Haru does not want to stay as a cat forever, which would’ve happened if she stayed in the Cat Kingdom.