Wait is it the little girl is actually very scary one?
If you mean scary in a way that she got so fed up being roped into passing the love letters to her brother and everything up together. Then yes, and i dont remember the details but i felt like the uke thought the sister was actually scary?????
Ahh I guess we're thinking of different manga
I thought about this one
https://www.mangago.me/read-manga/ore_no_aoharu_wa_watasanai/
Awww, thanks but it's not this one either but i'll read that. Thank you!
From the comments, it reminded me of this one! https://www.mangago.me/read-manga/kimi_towa_gokai_kara_hajimarimashitaga/
Seems like one of my fave.
Kimi to wa Gokai kara Hajimarimashita ga
Help, i felt like i already read this but then i feel like its another manga??? I can't remember the title, help meee. It has similar plot like the uke mistook the seme as the girl he liked and all. But turns out the gurl and seme are siblings