@Shelly That is a great theory tbh.
But theory aside, this universe is truly scary, basically, the BL universe has been pulling the strings behind his back since MC met whit Hatano wen he was a kid, so we can safely say that the BL universe doesn't create simple cliches based on where the MC is at the moment or specifically whit randoms, it can literally set flags and keep pulling the strings on the MCs back for YEARS.
Literally for YEARS the BL universe was preparing this 1 dude just to use him against the MC, and it even menage to for the first time stalemate MC, its the first time we can say the BL universe won, MC didn't manege to avoid the cliche and instead delayed it.
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BUT, what if Hatano honestly fell in love whit MC at random whiteout the help of the BL-verse ? Maybe the reason why MCs tactics did not work on him and a stalemate was reached i because this isnt a BL-verse made cliche ?
Lemme try to explain:
All of the examples we were shown during our journey, has the MC avoid cliches by showing that he knows how the cliches work and how to avoid them (aka: being self-aware), leading the "love interests" thrown at him into someone else, but in this extra, the MC tactics did not work at all, he used the appropriate tactics for the right cliche, we even saw ir during chapter 19 "Flag", and yet he failed and ended up whit a stalemate, whit Hatano still liking him. (Plus, notice how there was no "BL File" at the end)
Now, it brings me to the real theory:
MC believes this universe to be a BL world, a BL-verse, BUT, we know for a fact that straight couples do exist, so, we can guess the BL-verse does not target every guy on earth, and therefor some guys do end up whit girls and have kids, so if we know the BL-verse does not affect these straight couples, it is not far-fetched to assume that there has to be an actual gay guy the BL-verse doesn't affect, so, therefor, despite this guy being in a cliche, it isnt a artificial one made by the BL-verse, and therefor not as easy to escape, as the love behind the cliche is real, and therefor MC cant just make Hatano like someone else like the MC did in the previews chapter "Flag", since that is not how love works.
So yea, that is my thought process, I think the MC is so set on seeing everything as the work of the BL-verse, that he started seeing any gay relationship as a setup from the BL-verse, wen there are some who the BL-verse does not affect and are just into guys. (I suspects the brother isnt also affected by it, seems weird the author would just give us his perspective for no reason)
I kinda believe that this extra was literally the author setting a flag for us on who the MC will end up whit, plus the MC weirdly sought further information on Hatano despite he never doing so for anyone else.