general jack of the sith empire wanted to win over mitsutaro nan as his subordinate, but mitsutaro refused, so general jack transformed him into a power to destroy it. when the transformation function is destroyed, mitsutaro is thrown into the universe. when it was about to become cosmic dust, kotaro was shining with the mysterious sunlight, and the imperial stones in his body also changed. kotaro also became the new prince of light, "son of the sun" kamen rider.
