Kuroi Souya is a high schooler living a peaceful life despite having no memories of his past. One day, however, his town is attacked by one of the mysterious Nebula Weapons. Together with the cat-like "Sensei" and the gothic lolita Ginko, Souya gets dragged into a battle against... seven superheroes who protect the town! What is Souya's reason to fight? The answer lies in his memories.
Summary taken from: MyAnimeList