To borrow Gen's wonderful phrase, the answer is Yes for Will, Charles, Sameth, William. Tumnus and Jane aren't the ones who will go into a fight but will stay beside you. Demeter's a goddess and has her version of yes to this. Moist will be somewhere across town or he might stay to help but violence makes his feet itch. The Pirate King has a much more conditional yes.

Will-Robin, the men of Sherwood, any of his friends in Milliways, most people in Milliways, he'll fight beside and for those he believes in. Every day he knows he might end up dying for Nottingham, its part of how he approaches the world.

Charles-Raven, Erik, Hank, any mutant he's met, his friends, but he'd much rather live than die for them.

William-his mother, Mark, Thalia, Katya, Michael Westen, other friends I'm forgetting, but he'd rather not die.

Sameth-His family, the Old Kingdom, Nick, Kait, many of his friends in Milliways.

Demeter-She's a goddess so can't easily die but she would risk herself for any of her friends and some of her family.

Jane-Her family, Tom, but dying for someone isn't a way she likes to think of the world.

Moist-No one, he'll help people out in a number of ways that aren't always obviously helping but he doesn't want any violence. If he has to say I'll die for you to prove his loyalty then he'll leave.

Tumnus-Lucy, the Pevensies, Narnia, Aslan.

The Pirate King-Maybe Ruth and some of his men but he'd rather not have dying be an option.