In the game, Hayate and the Heroines want to clean the Sanzenin family mansion's underground library. In the library they find a book with blank pages. All the girls fall into a dream world because of a curse created by Mikage Watarase. Mikage tells Hayate if he wants to wake up Nagi and the others he needs to enter and end each of their dreams. Hayate will face an adventure in order to wake the heroines from the curse.

[from Fandom]