Soya Kuroi lives a peaceful life despite having no memories of his past. But one day, his city is suddenly attacked by a giant machine known as a "Nebula Weapon". Along with the cat-like Sensei and the gothic lolita girl Ginko, he is dragged into the fight, but he ends up the enemy of seven heroes who are working to protect the city. What is Soya's reason for fighting that is locked deep within his memories?

[Source: Aniplus]