please help me remember this manga's name

[SomeoneUltimate]

there's this manga about a purple-haired girl who's calm and dense and a handsome guy, blonde and blue eyes who has a sister but more importantly he's trying to make the purple hair smile and it's just so cute

the side characters hmmm, there's one who like the guy and uses her boobs as an advantage, anyways i need your help!!!

 

[DiLiN264]

Could it be - Watashitachi wa Koi wo Shiranai? I'm not sure about the sister, but I remember the main characters and the side character mentioned.

 

[SomeoneUltimate]

@DiLiN264 yeees, that's the one! thanks a lot!