[@NightmareInd] That said, if you are joining we should talk about what the differences will be between Charlie and Rebeca.

As a starting point, I would suggest that Charlie can generate hotter flames, whereas Rebeca is physically stronger and has greater potential for general destruction (for example, you mention that Charlie has good endurance because he's partially made of steel. If Rebeca punched him, it would actually hurt). 

Unless Rebeca somehow manages to get her hands on the Red Orb and goes Primal. Then I'm afraid Charlie's just out of his league, but could at least withstand being near her. Unlike pretty much everyone else.