Rose is a mercenary of the Bulletfist clan, who will become one of the main cast next season.
She's extremely short tempered and often violent to people who cross her. Though she's not nessessarily a Tsundere, since she's not hiding her feelings behind anger; if she likes you, she'll say so. But that means her rage is genuine too.

Her developement mainly relates to the character Keanu for the first season.