Dream sans<3

In one AU, an entity appears that feeds on "false happiness": it disguises itself as a source of joy, but in reality, it drains the inhabitants of their capacity for genuine joy. Dream arrives there as a guardian of positive emotions and, at first, easily defeats minor manifestations of evil, but then realizes that the enemy doesn't attack head-on, but rather subverts the very nature of happiness. He is forced to confront the fact that sometimes "being kind" isn't enough: he must see the lie behind the smile. (The ending can be varied: either he finds a way to restore true happiness to people, or he realizes that goodness isn't the absence of pain, but the ability to remain bright even when things are hard.)