The protagonist is a girl(?) pretending to be a boy(?), she is currently acting for theaters or stage plays. She is also a genius at acting and whenever she acts, the actual scene will appear in the audience eyes, like she makes them hallucinate or something?

One scene is where a guy who's her acquaintance is dying and also a scene when the protagonist is acting a scenario wherein she's currently in a train, her hair is short there.

Sorry if the description is vague, too many years since I've read this manga.

sounds vaguely like Kasane (MATSUURA Daruma) ?

Maybe ACT-AGE?

That sounds like the "Galactic Railroad" arc of ACT-AGE.

That it! It's ACT-AGE, thanks!