I decided not to worry anymore about how many characters I have: there are never too many!
"Sonia" is Russian variation on "Sophia". Also, Sonia can mean "sleepyhead" in Russian. Sonia is a very calm female sika deer. She often looks sleepy and doesn't usually talk much. Her walking is slow and lazy but in danger she runs fast like any deer. Her laziness is unusual for a deer, it's probably more related to predators. It makes Sonia more assailable while other deers are alert and watchful.
But once you know her better, you can notice that Sonia's very pleasant as a person. She may be not a talker but she gladly responds to a friend... or if she's got what to say to a foe. But mostly Sonia tries not to quarrel with anyone, appreciating peace and comfort.