Amazing episode with some really superb direction. Especially the first henshin sequence where we see how the Orange Arms materialize in Helhim and opens a crack to arrive at Kouta's side. The sequence with Mai, Kouta and Kaito near the tree really shows how everything has changed including their relationships with each other and they really pulled off the sense of how desolate the city has become with this one. Again I credit whoever is directing. And of course they remembered the Kachidoki Bata attack from episode 24.
Why should Kouta be hesitating? To me this is kinda hurting Kouta's character development…
Because Micchy is his friend. He is not a corporate suit or a faceless goon or a guy in a labcoat like Zangetsu, Sid or Ryoma. He was part of Team Gaim for more than half the series whom Kouta and Mai trusted and considered one of their own. It would be ridiculous and out of character for Kouta to have him shoot Zangetsu in the face with the DJ Gun knowing full well who it was behind that mask.
Starting from Jinba Lemon to getting Kiwami Arms Kouta developed determination/courage to move forward and to confront anything without hesitation to save the world.
Kouta's determination has been since Kachidoki Arms was introduced was to prevent the mistake that he made in the beginning when he killed the Inves form of Yuuya and choose the lives of himself and Mai over that of Yuuya. The current situation essentially mirrors the one he was confronted with in the very beginning: facing a personal friend and member of Team Gaim driven out of his mind and bent on killing him, but he is forewarned this time.
And he is determined not to repeat what he did to Yuuya.
It would be even more out of character for Kouta to shoot or kill Micchy since that would go against everything he believed in and fought for.