But... we just had this same fake-out with him and his sister, no matter how out of ideas you are, you can't just repeat the same tired tropes twice in the span of 3 chapters. this was never a good manga but this is a new low
also how dare he ask the girl he's dating to go on a date?! shame on him !
Yes, obviously, it's her "brother", teaching her how to go on dates properly to give her confidence, in EVERY area, hahaha. I'd honestly prefer forced drama over blatant plot copypaste.
The only plausible explanation I can think of to make this blatant re-use of the same plot make sense is that it turns out after 20 chapters the truth of the series is revealed and instead of a benign, silly romcom it's actually a weird psychological experiment to see how readers handle insanity like telling the same story multiple times for no satisfactory reason.
Well.... that or the author is dumb and doesn't understand how story structure works. I suppose I've seen enough manga go off the rails to believe that there's a giant swath of authors who want to draw stuff but have no idea how to write and everything falls apart as soon as they have to flex those muscles.