Namaiki na Gal Ane wo Wakaraseru Hanashi - Ch. 58 - Part-Time Job 5

[Triake]

She's still his 1st Cousin which is classified as incestuous by most authorities that determine incest. People forget that she's related to him by being his Aunt's daughter (on his mother's side). They've also known each other since both were kids so even if your excuse is "well they didn't grow up together" it would be wrong.

Even if "most authorities" did argue that to be incest, it's not considered incestuous enough as first cousin marriage is legal in most countries. More importantly though, in their country it isn't illegal or taboo.

 

[ImabotStw]

So it's normal for a family member to be protective....

I'm sorry but since when unironic spying on your sister not only at her job but also following her to a bar in a disguise, a normal level of protectionism?