This is about as large as I expected the comments section to be for a chapter like this...it definitely had that "final battle" feeling where all the allies you've met before show up to fight together. As seen in VanDread, or the Avengers, or Star Wars. But this is about one couple on a train. I don't think there's any story quite like this one.
I've been thinking about why this is so appealing to me. I mean, obviously the competent writing is (sadly) a standout among a lot of stories these days. But beyond that, I think it's a meta-commentary. A lot of adults like reading about high school romances, because it's an exciting time you can never really recapture. This is a story not so much about that romance as about the people who enjoy watching it--it's even more targeted and relatable to the audience of people who enjoy high school romance than an actual high school romance would be.
While this was a climactic moment, we shouldn't make assumptions about how long the story would go. Jitsu wa lasted far longer than its flow would normally suggest, because new goals and developments constantly appeared.