Elf queen Hirana chose to allow white men to reside in her kingdom. But unbeknownst to her, white men have pheromones that cause elf females to be unable to reproduce with anyone but them, and increasingly unable to control their interracial lust. Female elves end up with the white men, and the two end up forming a strange new dimorphic race of their own.
The sub-scenario explores the society later on, where elf females affected with decades of white lust during their childhoods pop during puberty.