Tenkuu Senki Shurato

Shurato, a 16-year-old martial artist, competes in the final match of a tournament alongside his friend Gai when they're unexpectedly drawn into a massive ball of light. Upon recovering, they find themselves in a mystical heavenly sphere with an otherworldly atmosphere. Shurato soon learns he's the former king of this realm and has been restored to his true form. Gai, however, becomes hostile, setting off a chain of events that pits the two against each other.