The Sun is the center of the universe and in charge of the galaxy, long before the Moon Bear King concord the moon. The sun warned the Moon Goddess to beware of the dark side of the moon, however, she wanted balance between light and dark, which worked in the Moon Bear King's favor when he surprised her and shattered the light side of the Moonstone.
Sometime during the Moon Bear King's rule, the sun suffered from an "undisclosed medical problem". Pikarina, his daughter was worried, for without him, all will be plunged in darkness. She left to provide sunlight to the rest of the galaxy till he got better. She later ended-up on the moon after the other planets inform her that the Moon Realm really needs her help. This allowed the Moon Bear King to capture Pikarina, turn her into a pixie looking puppet, and keep her locked up so the sun wouldn't dare try to stop him at the risk of his daughter, but was later rescued by Kutaro.
During the game he was mention a few times but was first seen and met in Act 7 Curtain 1, after defeating General Monkey. Surprised by Pikarina's new form, though claiming he still loves her just the same, he tells Pikarina that she should have let the moon work out its own problems and that this is a galactic issue, and its not fair to pin it all on one kid to fix. He then tells Pikarina that he along with his body guards will have a "chat" with the Moon Bear King and save the goddess, to which Pikarina and Kutaro rejoiced! Sadly the sun and his guards came back after a few seconds with broken bones and bruises, the Moon Bear King's new power, thanks to the stolen souls of the children of the Earth was just too much. He then tells Pikarina not to worry, they'll find a new moon. Leaving once again Pikarina and Kutaro to face the Moon Bear King alone, he they gave safe passage back to the Moon Realm.