Protagonist

Isabelle Rivers is a serious, reserved ex-mercenary who has the power to transform into a catlike form (nicknamed "Cat-Tags"), in which she is more energetic, and can range from being a smart predator to feral beast. She was once in a mercenary group targeting the brothers, but convinces them to let her join them in their mission so that she has some asses to kick in the meantime.

She has a rather monotone voice in her human form, but has a more of a feisty voice in her catlike form.

First appears in Episode 3.