Set ninety-seven years after a nuclear war has destroyed civilization, when a spaceship housing humanity's lone survivors sends one hundred juvenile delinquents back to Earth, in hopes of possibly re-populating the planet.
Niylah ( Jessica Harmon ) was originally only meant to be in two episodes, but she wound up appearing in 32 across five seasons. Having not originally considered her to be a character that needed to be given much of a personality (if she really only did appear twice), writers ended up giving her essentially Harmon's own personality.
Bellamy Blake:
My sister, my responsibility.
English