The funeral marches from and to school were crazy. Imagine how long it actually took them to walk that distance (if it were in real life), and the thoughts running through Kasuga's head. The holding hands was like... it was like Nakamura was the only thing holding him together, as they shuffle slowly along home. The music on their way FROM school at night suggested a feeling of elation, maybe even calm. Like Kasuga was happy/relieved that he got those feelings out of his system, and that his classmates would FINALLY know the truth. However, god damn, he just had to paint over his name, his classmates are still in the dark, and thus perpetuating Kasuga's role as a "closet-pervert" for Nakamura to exploit. It's a vicious cycle where a person gets stuck in a particular way of living, a particular mindset or personality.
I don't know whether to classify this story as a tragedy yet, or what Kasuga's tragic flaw would be. Maybe it's Kasuga's attitude toward others.. he did refer to his classmates as "dumb slovenly seals" at one point. I guess if his attitude doesn't change by the end of the series, this story might end up a tragedy as Nakamura continues to exploit Kasuga's role as a "pervert" and Kasuga increasingly feels like he has no one to turn to except Nakamura.