A Single Snowflake of Love Falls: Forecast of Changing Colours

There's a jinx at Haruru's school - if a couple sees the blue train at 6 am together, they'll be together forever! But if a couple sees the blue train at 10 pm together, they'll break up!
Haruru is going out with Nagi, a boy who goes to another school, and their love is just starting to blossom. But what happens when Haruru happens to see the 6 am blue train with someone else?! (From: Nagareboshi Manga)