It's just the very last theory on this page (in the Other WMG section).

Okay thanks for that and.....

.... Well that is fairly dark idea but I would still find it interesting if it were the case you what with tying some events together and giving even more emotional weight to that event.

I'd actually be fine if they redid Gaim vs Baron only instead of fighting for one thing it's like the last day and they need the other's Eyecons.

What is Onari becomes Necrom. I would love that.

Wasn't it rumored that Necrom's evil?

I don't think that was ever a rumor, but don't quote me on that.

People generally associate the word "necro", in any form, with being evil. So a lot of people are just going to assume automatically that he'll be evil.

I bet that Ganma general is Necrom!

The Ganma haven't shown any more generals yet.

While it's true that what little we know of Necrom doesn't explicitly imply that he will be villainous, the fact that his motif (eye drops) is shared with the villains does sort of point in that direction. It's too early to tell, though, obviously.

The popular theory seems to be that Aran will be Necrom, and since Aran is apparently a bad guy, the theory is Necrom will be a bad guy. That's pretty much all it is, I guess.

Gaim's motif was shared with both the heroes and the villains, and you could argue that Chase, while he was evil, shared the shift car motif with Shinnoske before switching to bikes, and there's also the Delta belt, which for a time belonged to the villains. Name any other case where the villain and hero both used the same powerset. I'm just basing this off the rumor from that guy who called all of these saying that he'd be evil.