Okay, so for the two top ideas on secondary character themes I'm gonna go ahead and give you guys a breakdown of how it would go down in-game. Because these secondary characters will be made specifically to be a team together they have a specific type of set-up:

WWII Heroes: This idea will give you the most freedom in terms of how much you can do, dozens of characters to toy around with and come up with something. This group will come together as a support group for people with superpowers and when one of their own [an NPC] is taken hostage by one of the groups counselors they decide to put on costumes and rescue her [the kidnapped superhuman]. 

Thunderbolts: A group of convicts with and without superpowers will be approached by a shadowy figure and given the option of carrying out their sentence or taking down a few superhumans for their freedom. They're given the keys to the storage and evidence lockers where they have all of the criminals from the modern day Marvel U.'s weapons and gear/costumes at their disposal.

So... those are your final options. I sort of know who I'd pick either way but I leave the decision about the theme in your hands. 

~KL~