I'm looking for something Vikings or Assassin's Creed: Valhalla adjacent for my merman! The basic idea I have is that a Viking clan is either raiding (or being raided by) another settlement. The clan placates the gods of the sea for their favor, trying to invoke favorable weather or storms against their foes, et cetera. In traditional Viking fashion, they choose a warrior/raider to be sent as an offering to the Sea. This man may believe he's intended to be a sacrifice to win the favor of the gods, but the envoy of the Sea has other desires. Happy to include other supernatural influences and flesh out the idea together!