In episode 2 in Koro-sensei Quest! Class E ventures into a northern cave to recruit Karma, a powerful but sadistic student, to join their quest by convincing him to level up with them, as they aim to become strong enough to face the main antagonist of the game

Everyone was following Koro-sensei, to find the "red devil" in the cave he lives in, it feels easier since Korosensei is leading this

Then in the dialog box text appears saying: Karma was fascinated and intrigued by Aku