Was it really a love song? or was the bully guy just saying that? To be honest I think we should have had some sort of internal monologue about sexuality or them wondering if the feelings are romantic. Even Aya doesn't seem to have given it that much thought she was like "oh my crush is a girl, well okay" but hasn't made a move and neither has she exactly been in denial either. But at least with Aya it seems to read as though she doesn't want to ruin the friendship, as for Mitsuki... I'm not sure what she's thinking at all. I mean are teenagers in Japan already so comfortable in their sexuality that they kinda take it for granted that something is romantic without talking about it? lol not even a "do you like girls?"
So, Japanese culture is by a wide margin the most intrinsically passive aggressive culture I have ever interacted with. The typical way you say something is "bad" is to say "That's a little..." and just literally trail off without saying it. As a general rule, they do not confront issues head on. So a lot of yuri manga doesn't confront the idea of homosexuality head on. The women just love each other, and their preferences aren't usually explicitly addressed because Japan in general isn't very hot on explicitly doing anything. I don't know if this also permeates into LGBT social circles in japan, or if it's just an anime/manga thing. It could just be that it's about anime authors not wanting to alienate potential readers by being too direct about their subject matter, or it could be that many people in japan just don't voice their preferences in a direct way very often. (If anybody knows more on this I'd be interested to hear it.)
This observation seems kind of limited to the yuri manga of the 2010s and 20s; after all the ol' reliable "but we're both girls" trope that everyone loves complaining about (and isn't nearly as common today as its opposite: "we're both girls so it's fine") is a confrontation with homosexuality. The Class S literature from the Taisho era (the predecessor of the yuri genre) had to 'balance out' depiction of attraction/romance between girls with tragic endings, which I'd also call pretty direct.
But even in the yuri manga of these days, the topic of lesbianism and queerness is not actually a taboo across the board; the level of openness runs a wide gamut. There is a branch of yuri where the same-sex nature of the relationship is so trivial as to be dodged completely - this especially applies to "404: men not found" and a lot of laid-back slife-of-life works. And the kind of works where concepts like 'LGBT' and specific identity labels are discussed at length (like they are in TsukuTabe) are rare. But there's a lot that lies somewhere between. For example, by filtering for lead or key supporting characters who are noted to be lesbian or attracted only to girls, there are quite a few series that have been adapted to anime: Sweet Blue Flowers, Whispered Words, Kase-san, Bloom into You (Sayaka), Otherside Picnic, Yuri Is My Job (Nene), MagiRevo, WataOshi, The Moon on a Rainy Night (upcoming). And these are just the tip of the iceberg. A more direct approach to the subject is especially common in series with adult leads or a historical setting.
