Let's be frank: Shikou is already a villain, he's just a benevolent one. He's got a space god or something inside of him that basically already won, and it's only because Shikou's more reactionary than active that he hasn't really done anything on the megalomania part. As a result he becomes more the enemy of other villains because those villains are trying to ruin what he sees as his responsibility.

Other characters most likely to be villainous are Souha (cause really it's amazing they haven't snapped by now and just tried to burn down the world in a blaze of glory) and Shinji (for REASONS).

Hilariously enough on the other hand, neither Shian or Sanshi would ever be villainous, despite being DARK-sorts and generally having a lower moral threshold. In fact, they're more positioned to be protagonists at this point! But on that same note due to GX's whole "nurturing darkness/light of destruction" deal, neither Setsuo or Sadame would be villainous either, despite being LIGHT-types-- they're just a little bit on the wayside of emotionally unstable.

Does Saiga ever accidentally remind herself of all of her bad decisions and desire to hit her head, or does she get out the overcoming wave of stupidity shame by doing something more constructive.

Also does she have any pictures of herself of around when she just entered DA, and get regularly baffled at the differences?