Mirayarus
"Oh mighty sun, burn the creatures of the night from this land while I enjoy coffee and bacon."
Marika - at one point, was surprisingly human. Not born with a tail and horns. Surprised, aren't ya.
The answer to this is a demonic entity trying to possess her body. Now you might ask, 'when why how'. The when was years ago when she hung out with the wrong crowd. Why is they were secretly trying to use her as a vessel for some evil entity. How? Well, she was a little bit stupid... Marika is now evidently in control of her body and mind, taking on the pale skin and demonic features and those weird glowy eyes. Oh, and she's scary good at playing the guitar. She somehow called down lightning once while playing a riff. The smell of burning flesh followed her for a week.
Currently a hero(?) under the watchful eye of her boyfriend, while not saving civilians from the inevitable Purple Ganger, or perhaps the pesky PSI recruiter, she leads a band called the 'Kallokatkaisijat', or 'Skull Breakers' in English. With her are backup guitarists, and a drummer. Her ego is already inflated into the ocean because she has her fronting position as the main guitarist and vocalist.