I can't say to much without causing spoilers, but I can ramble a bit.

Oya is a witch and Myka is her familiar. (Jute is the salamander in the sphere aquarium)
she is 100% human looking, the slippers and plushie tail are enchanted to make them look real, but no there just accessories. Simple reason for them Oya is sometimes a big kid and thinks there entertaining. The tail also helps with balance on the broom. (yes she rides a broom, but more skateboard style instead of sitting on it.)

Myka can talk telepathically with people he's established a link with, meaning not many people. Not much is known about Myka before he found Oya and became her familiar. Only thing he ever really mentions is that he had to wait a really long time for Oya to be born, so who knows how old this strange cat really is. He appears to be a normal Norwegian forest cat though, but as with many things in the Sen universe looks can be so deceiving. Myka also seems to carry a bad grudge against demonics, not demons just demonics. Last notable things at this time is Myka never seems to age an is able to use magic himself.
random facts 1. Myka is Snarf's father (Zero's cat) 2. Myka does in fact know Magical Mr. Marlyn Marvelous Mooncat, there old friends. Myka quote, "I knew him when he was just a normal kitten when he was just Marlyn not magical marvelous or a mooncat."

an Jute doesn't need to eat or anything he's technically a "zombie" in the sense that he died way before he got put in the sphere. So being shook about doesn't bother him except for maybe making him dizzy or irritated. He can't talk, but he understands and is able to respond with body language. Oya can take him out of the sphere at will if needed.