"A long time ago... after the age of the Death Phantom, Queen Serenity was afraid that there could be other evil forces lurking amongst the mortal populace. So she gathered all of her energy and the Sailor Senshi, and purified everyone on the entire earth, so that the evil would not return."
Several hundred years ago, an entire generation of humans were purified. Purification leaves its targets without any negative feelings; a compulsory love of everyone. Million's of people's love for one another was wiped away into meaninglessness by purification.
The idea of loving everyone, on the surface, seems like a gift--not a crime. Purification, however, makes the victim love all human beings equally. If a person has been purified, they love their greatest enemy as much as their wife or dearest family.
Rather than vanquishing evil, Serenity created a generation of children with purified parents, who treated them the same way they treated anyone else. Many learned to accept this love as normal, but the naturally selfish love of children could not be satisfied with a purified parent. Many of them grew up feeling empty. Rather than creating a bright future, Neo Queen Serenity created a new generation of children who felt hollow and unloved.
Neo Queen Serenity, however, knew nothing of the repercussions of Purification. She believed that her actions were a blessing to humanity, not a curse. It is Seisui, enraged by the Purification of her father, that teaches the Queen the true horror of her crimes...