Fan Casting I Cannot Self-Terminate in Sort by Tropes

Perhaps the Body Horror has almost completely taken over a person, and with their last ounce of humanity, they beg to be killed. Perhaps they've just been wounded in a vital area and know they are going to die slowly and in agony, and just want to die with dignity/end the pain quickly. Perhaps they're losing the battle with an Enemy Within and they need the hero or sidekick to throw the airlock switch/fire the Forgotten Superweapon at them/lower them into the steel. Perhaps they are prisoners and being tortured, and the hero cannot break them free but could shoot them. In any case, while they're ready or even eager to die, they cannot do it on their own. This can also count as a Heroic Sacrifice, sometimes.