Demon Lord's Fable - Mythos Alpha
A regular class in high school gets warped to a unknown dimensional space by a typical summoning circle; where they meet the manifestation of an powerful being, bored out of it's mind.
The unique existence tells them that they are here to be his amusement, and will be teleported a realm called, Zaias. It informs them that one among them would be chosen as a main antagonist, in this case, the demon king. The rest would be summoned to a palace by a royal family of some random kingdom, as heroic saints, that would slay the demon king, or fall at their hands.
Calling this bs, the shitty delinquents of the class were enraged at this. They did this because tehy realized they'll miss the next gang war, next week or so.
Nonchalant as the being was telling the previous info, it ignored the idiocy of the delinquents and said the antagonist would be chosen randomly by spin wheel, and it would start now.
Here we finally see our main protagonist, or in this scenario, the "antagonist";