@xyzzy No one said it was right. If it makes you uncomfortable(nothing wrong with that), then don’t read it. I don’t have a problem with it just because it’s fiction.
Shounen grew some balls! And I think Onee-San is starting to notice his fidgety behavior.
We're so close to merging timelines with the author's doujin.
Given the expressions onee san made in this chapter I think she is starting to realize (or even already realized) shounen has a crush on her. In that case,the fact she accepted his invite might be a good sign.