Man, "Wicked" Iruma isn't a bad person at all. It's just that he's no longer afraid of everyone, he doesn't hesitate anymore, and he finally says what's on his mind.
The ring spirit gave him two things, a wicked phase and a personality shift. I can only see his wicked phase as him wanting to change something, so he wanted to change how everyone saw at his friends and classmates; Instead of being seen as a class of exceptionally bad students, he wanted them to be seen as exceptionally good, if quirky, demons. The personality shift was probably just removing his fear of being discovered as a human, not wanting to stand out, his hesitation to act, and to give him a self-confidence boost.