-( Story related, cannot be missed no matter how hard you try )-
You will require Bakugami's aid of the Cherry Bomb Brush Technique whether you realize it or not. The Pyrotechnist's Hut is only available after purifying Shinshu Field, and access into the building happens at night. Talk to him and he will pour out his woes, but make notice of the banner on the wall in the back of the screen. Once he has thrown an entire arsenal of explosives in the cannon, draw the same symbol that was on the wall to light up the night sky and awaken Bakugami.
It may not be obvious, but you will require this technique to pass into Agata Forest through Shinshu Field.