Youji 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: Youji 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?

This entry contains the following:
- Fastening Days 1 (1 episode) - Oct, 2013
- Fastening Days 2 (1 episode) - Aug, 2016
- Fastening Days 3 (3 episodes) - Sept, 2017
- Fastening Days 4 (3 episodes) - Dec, 2019