Tanezumi is arrogant and pure evil, wanting to see people destroy and kill each other. She likes to make jokes, usually making jokes out of serious issues (IE the "We Just Found A Body" song she sings during an announcement she makes when they find out one of the contestants in Getting Out Alive are dead). She's also very flighty and easily bored, constantly changing rules and switching things up (very apparent in Getting Out Alive Chapter 15-17).
It is unknown what her beef is with Uncle Grandpa, but she stated in Getting Out Alive:Intermission 1 that she came from Japan. She moved from Japan on a ship to a small town in Michigan, US called "Noir Town", in which she states she burned down all the residence for making her feel unwelcomed. She apparently has affiliations with the Revolution but is getting paid by Ursidae Congregation to do their bidding. It seems her loyalty lies with whoever has the most money.