They're more tricksters and pranksters than evil, but they can potentially be evil.

[But as for the trigger.]

It depends on the demons, I think. Some just have fun killing people, others...like eating [Yeah, ew.] and there's some who killed their summoners just so they can roam around freely.

[He watches her hand movements, before his eyes moves over towards the floating snow in front of his face. And it falls.]

Some kind of ice magic?