Redemption Between Light and Darkness

After defeating Belial, Sero doesn't leave. Instead, he spends a few days playing around on Earth, and by chance is chosen by Saga to start over and save the darkness.

But later, the balance between light and darkness is disrupted. Thanks to the efforts of the New Generation heroes, all the villains embrace the light. After that, the only option is to have the New Generation heroes play villains, acting as heroes on one side and villains on the other.

(But later, the charade is over. I'm falling into darkness for real. Going back and forth pretending is just too exhausting.)