Incredible events between Hanako and Aoi, so
The way she took it upon herself to speak out to him on the train, he is her literal fellow traveler (because there is such a term "to speak out to a fellow traveler". This is what Mitsuba and Kou started with, but they deviated from their original goals). And they talk not because they are so good to each other, or that it is easy for them to talk about it, they simply have no one else to talk to and now any conventions do not matter.
How quickly Hanako noticed that Aoi is not herself because of the potion, although he has almost never communicated with her, but he has experience in similar situations with other people. He is an old ghost who can read people in a jiffy, this has been shown more than once. He is not perfect in understanding people and himself, but he has a huge advantage in the form of 50 years of experience.
How Aoi quite easily blurted out to Hanako something like "we are similar", and of the two of them, she is the one who says such things. This a shady guy who can hardly be trusted. And she, who never talks to anyone, even to herself, prefers not to do so, but the situation is at such a point that now she doesn't care?? She went and said it, and when she returned to her usual conditions, she kept quiet in front of Nene and Akane. And Hanako, of all people, heard what they didn't hear.
A funny scene, but with content that only the pairings Aidairo likes have, that are canon, almost canon, or could have been if the situation had been different. And for some reason Hanako and Aoi also have a scene like that, lol, a harassment scene and an almost-kiss. They, of all the characters, are some kind of incredible irony or something. They are in the game too.
Well, what a situationship, or whatever it is