Not really. She's not his sister. As far as we know, he doesn't have one. So how is he supposed to know how a little sister acts? He cares but it's 100000% understandable that he doesn't think of her like that. Add on that she's actually his oshi. He's acting just fine. Well... except for the "I'm gonna die if my oshi talks to a male" behavior. GTFO with that haha.
Did you note that I said "older brother FIGURE"???
They grew up together. On his end, she is for all intents and purposes his little sister... he views her as such.
He views her disgust as the actions of a little sister going through puberty than as real disgust. Basically, he doesn't take it too seriously. It's his view of a rebellious phase.
And he was also bothered by the girl he viewed as a little sister having a boyfriend...
Ok, so a girl who not only verbally abuses you, but also attacks your insecurities, you're gonna tell me that you'd instantly pick up on the fact that she's into you?
If you say yes, stop the cap
Crazy how you put all the blame on the MC but ignore the outlandish shit she says to/about him
How's he going to get a clue when you're so mean to him?
Even if she wasn't mean to him, he'd still probably never pick it up. They grew up together as family, so for him, she is basically his little sister.
It's also why he puts up with that treatment. He doesn't take it too seriously because, in his eyes, she's only just being a bratty little sister that he doesn't need to take too seriously.