Why Look for Reverse Harem in the Apocalypse?

Simultaneous rifts and the emergence of monsters. In the midst of a chaotic disaster situation heading towards destruction, Doya was living a bizarre, abundant, and safe bunker life, aided by a system that appeared from the start. "W-Who are you?" That was until four handsome, well-built men suddenly appeared before her. [The game scenario has been changed from 'Disaster Simulation' to '(19+ Only) Romance Simulation'.] [All romance targets have been encountered! The main scenario will proceed automatically upon completion of the conditions.] She tried to respond appropriately and quickly send them away, but only for a moment. For some reason, she's convinced these people won't harm h...