Ardyn somehow forces Noctis and Prompto into a situation where they have no choice but to have sex with eachother. In front of Ignis and Gladio who they are, respectively, in relationships with.

Bonus for Noctis and Prompto being really upset because they feel like they're cheating, even though Ignis and Gladio have said they won't hold it against them.

Double bonus for conflicting feels good-feels wrong feelings and someone (everyone?) getting turned on and feeling bad about it.

Triple bonus for the it being over and the couples trying to comfort each other.