.
Actually, the basis for the "monomaniacal immersion" (meant, in the original context, to describe the mangaka's artistic angle/execution) is... 16yo hormones.
Also the other thing covered about a billion times over: Tropes... combo, mind-numbing, hackneyed character tropes... But primarily, the "opposites (attract)" trope as the fulcrum of the basic narrative.
What's a tad bewildering--apart from fans/haters still latching onto these characters and expecting them to act realistically for a Manga-format Dramady--is the gratuitous memory decay (in general, but in this case, for a phase most humans have undergone/will undergo in life). While notoriously unreliable when colored by tremendous amounts of Emo, memory (in some shape or form) is usually clearest during those biologically heightened phases of life--unless there's gratuitous substance abuse and/or compounded trauma making it fuzzy/absent. Even if events and specifics are all askew, most people recall the personal side of Emo more than anything else. e.g., Catalyst A made them feel like (simple/complex) Emotion B, and they hated/loved it for C amount of time. Does no one (in retrospect) recall insta-lust and crazy infatuations with every kind of this, that, and whatever--especially tempting, compulsive shit that could get incredibly messy, in all ways, and later involve weary authorities? Triggers were/are abound: it doesn't even need to emit pheromones, and someone, somewhere is hooked, then restraining orders et al are pending; many people don't come out of this haze even in mid-life and beyond--although by then, it's more psychological than hormonally propelled.
There's nothing confounding about how or why Yuzu developed feelings for Mei since 1) time-honored types and related tropes for the series' premise, 2) the entire series is about the journey--stemming initially from hormones (bolstering idealistic love) with subsequent heavy-handed-complex-Yuri-wake-up-call, and 3) the lopsided, agonizingly OCD/slow development of an actual relationship that hasn't gotten all that far by many modern standards. How one defines the type of "love" achieved is entirely subjective.
And there you have it guys... Cased closed.
