You Give Your Firstborn to a Demon

Outcast from your village because of your affinity for witchcraft, alienated from society, you spend your time desperately looking for crossroads. One day, you stumble upon yet another crossroads far away from civilization, and feel a tap on your shoulder. You turn around to find a demon looking for an easy target. You offer everything you have, and everything you don’t have… but the only thing the demon seems interested in is your firstborn child. You’re desperate. Not questioning it, you agree. What was it that you so desperately needed?