Fastening Days: Yoji and Kei, a boy and girl, live in a town in the not-so-distant future with their foster parent, Anna. But these seemingly ordinary children have a secret hidden even from their unsuspecting mother. Yoji and Kei are superhero defenders of their town! With a flap of their capes, the two of them and their robot bear sidekick, Oscar, protect the citizens in their town with their handmade high-tech machinery. But from what menace? And will our little heroes be able to overcome the crisis about to threaten the town's peaceful everyday serenity?