Mr Ra is a bottle of Chili Oil.
Chili Oil is called Rayu in Japan - that's where his name came from. However, Mr Ra's Chili Oil is rather Chinese style and is hand made by Gyoza Otoko, the head chef of Pankichi-ken.
He is always angry, which is understandable considering that he keeps very hot chili oil in his stomach all the time. What will happen if his stomach becomes empty?
As his Chilli Oil tastes so delicious, he suffers an unfortunate event. But hope he is OK!