He notices her almost immediately, as she had gotten on the train seconds after he did. He looks at her once, then again. He notices that this girl is pretty. She is youthful, in her early twenties, or maybe even her late teens. Her face has a roundness to it and her chin is not perfectly defined, but she is not overweight. Something about her keeps him looking...
After a few moments he finds that it is very hard to take his eyes off of her. The more of her he takes in, the more he realizes she's beautiful. Her curly, shiny brown hair flows around her neck and shoulders. Her eyes are a pale bluish green and her irises were unusually large and black, even though the light in the train was ample. Maybe she was taking in as much of the world as she could, taking in its beauty and using it for herself. Her gentle and youthful features and her eyes make it very hard for him not to stare at her, this tragically perfect stranger. Their eyes meet a few fleeting times, so he tries to stop staring. But he does not want to. He looks upon the window he is sitting next to. There she is, almost a perfect reflection of her is there thanks to the deep black of night beyond it.
Ah, her reflection is safe. He stares at it, gulps as much of her down as he wants to, as he can. He droops his head to the side, rests it against the window, and just looks at Beautiful Girl Backwards, and dreams of a world where he has the nerve to go up to her, tell her how beautiful she is, and they have coffee and talk for hours until the sun rises. And then maybe they share a kiss for breakfast.
But that world is not possible, for many reasons. He thinks of them as he notices her gentle, warm smile. All he can do is safely stare at her ghost in the window as she laughs and smiles with her friends. Her social interaction seems very friendly and happy. She probably has a wonderful personality to match her looks.
The funny thing is, he does not think of sex once while he looks at her. Sure, when he sees attractive women he thinks about how great it would be to make love to them, or screw like bunnies, but with this girl, sex does not enter his mind. Maybe that breakfast kiss would be nice, but all his mind wants to do during the train ride is consume as much of her beauty as he can before he gets to his stop. He does look back at the real girl now and then to revisit details not clear in the reflection, like how smooth and silky her skin is, how delicate yet strong her hand looks at is grips the metal rail above her. Her fingernails are very short; they do not even go beyond the flesh of her fingers. So she's a nail biter. It may be her only flaw.
It strikes him, as he safely looks back at her reflection, how natural her beauty is. She stands next to her friends who have caked on the makeup but only look half as pretty as she does. Her cheeks are rosy, maybe that's natural, maybe she has put on some blush, but other than that it appears that she has no makeup on at all. She wakes up beautiful. He smiles when he thinks of her waking up in the morning, cracking her first smile as she greets the sun.
He sighs as he realizes that his stop will come up soon and he will leave that train, and that girl, possibly forever, never to see her again, never to speak a word to her, and he will go back to his life and she will continue hers. All he can carry with him is the memory of her face, a memory he hopes will not fade away anytime soon.
No, screw that.
As the train comes slows to a halt at his stop his heart begins pounding as it realizes what his brain is planning to do. As he approaches the door, and her, he stops. He looks at her. She looks back.
"I think you're pretty," he tells her.
For a fleeting half second he sees her face perk up, hears her say "Wha--" but he does not have time to see or hear anymore as he makes his grand exit as quickly as he can.
He knows he has probably made her night as he sneaks off into the night, away from the train, like a thief that has stolen a tiny piece of her soul.