I could be wrong but i see it as something cultural maybe? Ergh that isnt the right term but its hard to explain i detail right now lol. But in my family and so are my friends we usually dont show much affection but it doesnt mean we dont care. Its like embarassing and awkward to act sweet with a sibling.. more like a tsundere actually lol i cant believe im using that term here. But yeah mostly it is perceived that once siblings grew older they will like detach thselves and be closer to their friends instead like its part of growing up. It isnt just in anime or manga. And i dont think anime/manga like this one depicts sibling love as somehing impure. They just describe it in how actual siblings act when growing up. Like starting to get embarass being seen with them its not an act of coldness but just an awkward phase like how we sometimes growing boys or girls will get embarass when seen with their mom . Like they are still a child.
One show that perfectly depict my relationship with my older brother is ccs touya-sakura one. We call each other ugly or some other names, eat each others 'food reserves' etc.. but he still picks me up most if the time even if im already working.
Lol sorry i think im a bjt drunk so my thoughts are too jumbled.
How many episodes left btw?
It's not about how the sibling themselves act towards each other, I perfectly understand the whole being embarresed by them thing, I'm the youngest of six, and two oldest sisters embaressed me no end, and my older brother pretty much ignored me at school, that's part of being siblings. I'm not talking about relationships between family, that's an entire topic on its own,
The thing is how in Manga and Anime showing they care for their siblings brands them with a derogatory term by other people. Like if you actually show you love your siblings you have inpure thoughts about them, so you have to keep a distance.