"Contact," by Teramoto Kaoru:

Kaori doesn't know when it started, but she always sees a certain girl on the morning train.

The girl's name is Misaki, and she's told Kaori that she admires her; she's always hanging around her.

Kaori asks Misaki why her face is flushed, and Misaki says that she had to run to catch the train. Kaori points out that if they missed seeing each other today, they'd just see each other tomorrow anyway, but Misaki replies that every day is precious.

A guy has asked Misaki out, but she declines, saying that she has Kaori.
Kaori tells a friend about the situation. ("Going on about your love life?" "No! I've got a problem here!")

Her friend suggests that she just run away if the situation bothers her, but Kaori protests that Misaki cries over missing her for just a few days. Things might change if Misaki got a boyfriend, but Misaki doesn't like guys, so that's unlikely to happen.

When Kaori sees Misaki with a guy, she realizes that maybe she was wrong about that. Misaki spots Kaori, and loudly calls out to her.

The guy gets off (he has to stop by somewhere); as he leaves, he quietly tells Kaori not to glare at him like that. (As you might imagine, he really pisses Kaori off.)
Misaki comments that Kaori is early today, and Kaori bites her head off, saying she told her yesterday that she'd be going in early today for extra lessons (a note at the bottom tells us that she's lying about having told her).
Kaori changes the subject, asking if that guy is her brother or something. Misaki says that they're in the same club,

and that she doesn't mind being with the guy because he's special. Kaori's friend seems to think this is good news, but Kaori doesn't think this particular guy is right for Misaki.

The friend asks if she's jealous. Kaori denies it, saying that she just doesn't like guys like him. She insists that's all it is, though Misaki's earlier words about him being special echo in her head.

Misaki's running late today, so she's not on the train with Kaori and the guy. When Kaori mentions this to him, he tells her that he already knows--in fact, he even knows why (morning tennis practice ran long).
Kaori had no idea Misaki was even on the team.
The guy also informs Kaori that Misaki's been riding the train twice every morning to see her. Kaori protests that she never asked Misaki to do that, to which the guy gives her some unsolicited advice:

at this rate, someone else is going to snap Misaki up. He gets off the train, but Kaori follows him. Kaori insists that she doesn't have feelings for Misaki and that they aren't going out or anything. The guy replies that if she really doesn't care, she should set Misaki free,

because empty kindness will only hurt Misaki.

It all started on Kaori's commute to school. The scenery was the same old thing every day. There was just one section that was special to her--a place where she could see the sea. So she noticed right away

that this other girl (Misaki) liked the same bit of scenery.

Kaori tells the guy that she can't push Misaki away--Misaki means too much to her for that.

"Sorry," she continues, "you can't have her." But the guy isn't interested in her anyway--he was just helping Misaki out. She's been standing nearby, listening to their conversation.

The guy points out that Kaori hasn't been honest about her feelings, and that just following the other person's lead all the time doesn't lead to any progress.
Kaori repeats that she won't let him have Misaki, and he replies that he has a boyfriend.

(Kaori wonders what sort of club they're in...)
Misaki tells Kaori that she's happy about what Kaori said before. Kaori's still a little mad that Misaki didn't tell her about tennis practice, but Misaki didn't want to inconvenience her.
Kaori thinks to herself that maybe she should take the lead sometimes, instead of just being the submissive partner. She asks Misaki to come look at the sea with her next Sunday--in person for a change, not through a glass window.