Ritsuka was formerly a spirit animal to Chii, but is now a Soul Bounder to Chii. Soul Bounders operate solely for their masters and have a built in instinct to listen to their master unless it places their master in danger. Ritsuka's no exception to this, but it's not just instinct that tells him to look out for Chii but his love for her. He loves to play with Chii, and this is something that is unlikely to change. Ritsuka takes on the appearance of a black panther with dark grey chest fur colour.
Even when Chii lost her memory for a while, Ritsuka stuck with her. His loyalty is unmatched. As soon as Chii provided a chance to get close again, Ritsuka tackled that opportunity right away. He is deeply satisfied to be close to his master once again.