A certain unlikely hero...

August 31. The day Accelerator meets a strange girl in a back alley and he's sure he's seen her somewhere before. The day Mikoto Misaka finds herself asked on a date by a very pleasant young man. That same day, Touma Kamijou awakes with an especially unlucky feeling. The reason: He's just realized he has completely forgotten to do any of his summer homework. Three characters, three stories, and one last day of summer vacation!