Chosen One

The Chosen Ones were human children that Fairies would protect and avenge if harm came to them. Eventually, the Fairies would claim these children and take them to their "Lost Lands". Once there, the children would be doomed to become Fairies themselves. The Fairies required these children to continue the existence of their race, despite being immortal (or near-immortal).

In 1909, one of Jack Harkness's soldiers accidentally killed a Chosen One in Lahore. In retaliation, the Fairies killed all his men, sparing only Jack.

In 2007, Torchwood Three allowed the Fairies to claim Jasmine Pierce as their Chosen One. (TW: Small Worlds)