I think the "end of the world" date is actually when Yura committed suicide. Everything we see up until near the end is most likely a flashback or a mix of different delusions overtime, with the ending of the oneshot showcasing how the guilt of ignoring the warning signs makes her feel like she's drowning. Like Glamour said earlier, it's her subconscious calling her a coward. Maybe the both of them did take a train to the beach and that's when it happened, so every July 1st she relives that guilty memory over and over again with the same ending.