"Women are calculating" "I'm bad at math, though" 😅
That said, why are you adding the little sister romance? If this is going to be an actual harem, sure... but she's obviously added to make this into a traditional harem manga... which is dumb... love triangles are bad enough.... we don't need a half baked imouto romance that's added to pad things out...
The fact that you are using the little sister character as mere padding is just wrong author-san... it's just wrong >.<