As you should already know, Aura and Chibi are Lunar-Cats, which are creatures from another planet.

Here are the most important information about Lunar-Cats!

Lunar-Cats are the citizens of the planet, Lunaris.
They are creatures with half cat and half human features and can shapeshift between Cat- and human form.

Their true form is their human form.

There are different types of cats, living on this planet.
There are mostly normal cats, like the ones which can be held as pets at home, on earth.
But there can also be big cats, like Lions or panthers.

For example :

Queen Reiko is a tiger.
King Leos is a Lion.
And the two princesses Rin and Sarah are actually normal cats.

What type of cat it is, is always a coincidence.

The Lunar-Cats know both magic and technology.

In their human form, they are not fully human.
They're more likely Nekos.