savior sibling 

A sibling that is born to give their organs, bone marrow, and basically anything that can be used to save the sibling that was born before from a terminal ill ness
So basically they’re trying to save one kid by using the other and a lot of it is not consented by the donor sibling it’s self

My friend is being used as a savior sibling against her will

savior sibling by Wisper and crispy February 3, 2020