Sometimes you get hero medals in battles right? Well. When you will have enough medals, heroes will be marvelled by your feats and will join. By the way, I think that you could soon get Rufus, one of Axl's friend.
Don't judge a book by it's cover Sam ehehehehehe… Dumb or not, I'm sure that Rufus is good at battling. Let's convince him to join us with those Rufus Medal