Some mechanic for Valkyries that involves escorting the spirits/ghosts of those who die in battle.

One take on this idea: you can chat to ghosts to tame them, and then they will follow you around as pets do. Then you can release their spirits by praying on an aligned altar. Doing this successfully gives you some sort of reward. However, hostile monsters will attack the ghosts you are escorting without provocation, making this not trivially easy.