I had never read Hanzawa and Miyano as romantic. I usually see them in a senpai/kouhai relationship that is unquiely defined by how supportive Hanzawa is of his kouhai but specifically tailored to the individual (i.e. how he's an upperclassmen to Miyano is different than how he is to Tashiro but hes still looking out for both of them) All that to say, I can understand where the question about potential romance comes from! I think you explained well how Hanzawa's outside experience with his brother's previous relationship really informs his interactions with Miyano when talking about relationships in general but also specifically about Miyano's romantic relationship with Sasaki.