Corruption

Bulletin Board #11 states the rule directly: increasingly powerful Vampirism abilities are gated behind Coen's Corruption, and Corruption rises through feeding on blood. A pre-beta build shows the rest of it — Corruption sits next to the health bar at the bottom of the screen, and it rises when Coen feeds. The higher it climbs, the more of the Vampirism tree becomes available to buy — each gated node states the Corruption level it wants in its tooltip, and an exclamation mark flags a node that has newly come into reach. Read it as a second currency with a moral price attached. Experience points are earned by completing objectives and are spent at shrines; Corruption is earned by drinking and cannot be spent at all — it only accumulates and unlocks. A player who feeds sparingly to keep their hands clean is also, mechanically, a player who will find the bottom of the Vampirism tree closed to them. That is the tension the night half of the game is built on, and it is why the feeding decision is a build decision as much as a story one.