I would like to throw in my own interesting theory. Something that several other people have suggested now is that we may have not encountered the champion. However, of course we don't know who the heck that would be because we haven't met them. Well... mostly. Ame being Ame, she tends to leave little gifts for those who are thorough enough to obtain them (Beldum, anyone?). I'd like to draw you attentions to a small post which has been over looked so far in this discussion. The "Favorite Character" thread on this very forum. Ame wrote, and I quote, "However my hands-down favorite character is Fer-- oops, that game's not a thing yet, nevermind~" (my apologies for not doing an actual quote. I'm on mobile in the middle of class atm). She also later wrote on the same thread, "oh dear god i wasnt even thinking about that, i promise it is not fern or anyone remotely like him." This leads me to believe that the mysterious Fer- character is honest, straightforward, unwavering, and gentle as those traits are the inverses of Fern's own.For a character to become the game creator's favorite and be that developed, this mysterious Fer- simply must have a decently large role and has also been yet to be unveiled. Based on what we know of the game, there are only a few of these roles remaining. The most prominent and obvious one is, of course, the champion.
Of course, I could just be connecting the dots of two different drawings, but hey, a little speculation never hurt anything, right (well except McCarthyism, but that's another story)? I do realize that she wrote "that game's not a thing yet, nevermind~" but she still wrote it on the forum thread relating to listing one's favorite characters in the Reborn game itself. Anyway, I hope you enjoyed my speculation. Feel free to pump it full of lead, if you so choose. It's all up to you, but regardless, I would personally investigate Ame's posts around the site to see if there are any potential dark secrets to bring to light.
Or just watch as Ame reads this then edits out all potential spoilers out of her posts.