No, this is when she understands that her heart fell for him a long time ago...1, but her brain was locked in on "S█X", so it took her heart a while to beat it into her brain.
1: Chapter 1, page 18 (which is page 20 as Mangadex counts them...)
Eh, more fun if she slowly changes as her power grows, e.g. streaks of purple in his slightly-longer hair as the transformation begins to... stick around, even when powered down.
She realized that, while she absolutely wants to climb him like a mountain and capture his flag (so to speak), she's actually grown to care for Kumasaka-kun as a friend.
I sincerely expect that, much like Yuri's Sides drive her to closer to insanity, Kana will manage to just barely hold on thanks to Octopus-Sausage-impact!Kana giving her a well-timed push on the Mental Plane at a key moment. Something along the lines of "No, you have to bring 「My World」 into...
BSS, short for 僕が先に好きだったのに（Boku ga Saki ni Suki dattanoni lit. "Even though I liked you first" ) refers to the feeling of someone you had a crush on (but with whom you DID NOT have an established romantic relationship) going out with someone else.
I mean...
She wants to be a serious dungeon explorer, right?
Surely providing aid to others who have gotten in over there heads is just good etiquette?
and Observing Oji-san at work is just good sense!
Presumably John Dinne is Brainrot Girlfriend's Soon-to-be-Boyfriend. The name "John Dinne" may be a "Dark Past" e.g. Morisummer-> Nibutani Shinka, Dark Flame Master->Togashi Yuuta
Hybrid Vigour, further intensified by Tanya being the spiritual child of whatever Dad is...
Long story short, the kid's well on the way to being a Shonen protag.
Idiot. Your own self-assigned responsibility is to return the body to its original owner without letting any of his precious persons know that you've replaced him. If nothing else, use it to maintain the facade.