Lucid dreams.
Dreams where you know that you're dreaming.
After an accident in his youth, Tooru Naitou began to have nothing but lucid dreams. Always being aware of when he's dreaming meant that his mind could no longer rest when he was asleep. Only when he collapsed from utter exhaustion does he finally get a reprieve.
Lucky for him, he has a childhood friend, Saki, who insists on calling him 'Nii-san' that tries to do what she can to support him. In his science club, his senpai Yayoi is endlessly amused by his awkward way of living. And he has an underclassman, Keiko, who likes to sing in front of the station and likes to call him weird for his less than normal attitude towards life.
Tonight, Tooru dreams again. But this dream is different from those that came before.
"Maia...? Why are you in my dream...?"
A girl he hasn't seen ever since he started having lucid dreams, and to Tooru, this was the very worst form she could take. But Maia wasn't the only one who appeared.
"I'll put an end to bad dreams right here."
With those words, a girl who calls herself Alice rescues Tooru from Maia's grasps. Alice says that she's a traveler of dreams, and now she's come to Tooru's dream. What could all this mean? The anxious Tooru certainly has no answers as Maia softly whispers into his ear:
“This is the story of a sweet, happy nightmare.”