If We Don't Get Married, the World Will End summary: Leona, the first woman ever assigned to the Special Forces Central Division, ends up partnering with her mischievous academy rival, Regan Crawford. The two, who never quite got along, are suddenly approached by an angel named Sylphion, who delivers a shocking revelation... Their future child is destined to defeat the Demon King and save the world. Having kept their distance from each other for years, Regan and Leona both declare that if marrying each other and having a child is the only way to save the world, they’d rather just defeat the Demon King themselves. The angel, bewildered by their stubborn resolve, happens upon “dimensional streaming” and meets the constellations. Intrigued by the unfolding drama between the two, the constellations decide to help the angel weave a bond between them. To make the two fall in love, they begin crafting romantic situations across the multiverse. But things don’t go quite as planned...