One night, an interesting visitor appears in Koyori Aisaki's dreams - her good-looking homeroom and English teacher, Mr. Grimme. This is not the Mr. Grimme that Koyori remembers, though - what's with the knight get-up and harsh verbal tone? On top of that, what is all the nonsense coming out of his mouth about Koyori's dreams being "dangerous?" The fact is, Koyori does indeed have dreams of her own - except she's all but given up on them. What she doesn't yet realize is that giving up on dreams paves the way for darkness to turn those dreams into nightmares! Enter "Knightmare," guardian of dreams, who arrives once more to exterminate nightmares as only he can!