Let's start with the Mecha that the girls have for combat. In Japanese it's Mashin, which can be translated in two ways one is "demon-god" and the other is "machine"; trust CLAMP to make it double intended.

Hikaru's mashin should be a lion, because, if Umi's name shows to a dragon and Selece is a dragon, and Fuu's name shows a bird, and Windam is a bird, then Rayearth should be a lion. But it's a thing between lion and wolf and also unicorn.

Rayearth is a spirit when Hikaru first meets him, and appears in front of her as a lion/wolf/unicorn hybrid putting her on a test, to see if she is worth of commanding him. After that he takes a form of a mecha, dominant color naturally is red and gold, like his master, being a creature of fire himself.

When there is great need, the Magic Knights can use this and make their three mashins become one, taking various parts of Rayearth, Selece and Windam to become one bigger mashin, that has no name; even if people keep calling the big one Rayearth too.

Animalism (Lion + Wolf)

I'll just write a few words about this. As I already said, I think that Rayearth was intended as lion from the beginning, but I have no idea what happened in the middle with it. Anyway, both animals are a good choice when it comes to Hikaru and the fact that they personify courage, and stubbornness, and fighting spirit. Which is like a mirror of the red head.