I think the story is pretty much finished.
There was no hostility on the other girls' side towards Tsune, so I guess a back story isn't necessary. They were just puzzled when they saw her because she should be riding the other train, but she did so just to be with her senpai.
Then there's the crying of her senpai in the end, which I guess was caused by her seeing Tsune blush and the realization that she likes Tsune, and that she had hurt her by saying she'd marry for money. Just a confession and we'd have a happy ending.
Or I'm just reading too much between the lines and can't wait for the sequel.. x.x