"Surely, the teacher can't be the killer." I thought, thinking it would be more obvious than murder mysteries ending with the "
the butler/gardener did it" trope. After seeing the murderer and coming back once again, Satoru kept interacting with the teacher the same. Relieved, I kept watching, waiting for someone suspicious to appear. And then it turned out that it was indeed the teacher. Facepalming so hard I broke my neck finished watching it, which was a huge task in and of itself, as the last couple episodes were just boring once you knew who was the murderer.
And, finally, Kayo ending up with Hiromi just for Satoru to meet Airi again, who was not even in high school at that time made no sense to me story- and character-wise.