Riku

Origin
Riku grew up on Destiny Islands with his two friends Kairi and Sora. When a strange darkness came and took over the island Riku and Sora were seperated. Riku was found by Malificent who persuaded him to become an agent of the darkness. He did and was soon turned into a puppet by the Heartless Xehanort. With the help of Sora he counquered Xehanort and helped Sora and King Mickey lock away the door to darkness. He then set off on a journey with the king to save the world. He snuck around before finaling helping Sora defeat Xemnas for good. Riku also became a master of a keyblade shortly after the events up Chain of Memories.

Reasons for Joining Light Source
Riku knows first hand what darkness can do to a person. He joined along with Sora to prevent the darkness to gain complete control. Riku knows that it isn't the darkness that is the true evil its the fiends lurking in it.

Antics Within the Group
Riku is typically quiet but kind and well recieved by most of the members. He shows immense respect for King MIckey and his best friend Sora.