This here, is the Potato Prince, who is the brother of the Potato Princess, Chihaya, who both are next in line to be Potato King and Queen of Potato Kingdom. Although he may seem to be a bit strict, he is like that to take care of his dear sister that he loves very much, and does as much as he can to make sure that nothing ever happens to her. He even loves her to an extent to even make Potato Love with her.
He is also the winner of the Potato Kingdom Super Magical Potato Tournament, and the wish he made with the Super Magical Potato was that, no matter what happened, his sister will love him, and be with him forever. He made Potato Love with his sister afterwords. Don't worry, he used a Potadom for Potato Protection.
Although this article may be a lot about his relationship with his sister, it is usually all he thinks about, and most of the things he do is for the benefit of his sister, so it should be understandable. Anyways, he was once offered the title of Potato King, but turned it down seeing how his sister will end up marrying the prince.
He doesn't seem to have a noticeable relationship with the other members inside the Potato Castle, as he really only talks to the Princess. He may have small chats with other people once in a while, but that's probably just it.
One day, he hopes to find a place where his sister can live freely without having to worry about the trouble Potato Kingdom has.