These two issues are inherently connected, yet you keep insisting that one of the two is irrelevant. The age gap wouldn't be that problematic if it was a healthy relationship. Still unusual but better. The emotional manipulation would still be bad if the age gap wasn't a thing but it would be a lot less problematic.
Rin used the power imbalance and the difference in experience to toy with Ruka. She explicitly looked for someone less experienced, someone that would look up to her and trust her to toy with.
Except what you say completely ignores that we see Rin playing with
anyone she can, it was never simply about Ruka being younger or inexperienced, she was simply another victim in the long list of people with who Rin played with
Like, really, we're literally shown in the flashback how she plays with other people who are clearly inexperienced and that she has reputation of playin with people
You guys are so focused on the age gap that you're ignoring the rest of the context, that as Ruka says in chapter 19 pretty much sums it up,
she's not special, Rin has been playing with people for a long time cause she can, the only thing that really sets Ruka apart is that she's younger and who her brother is
Like, just reread chapter 41, we're clearly shown some of Rin targets were other students who had zero experience, who trusted her cause they thought Rin loved them and then she toyed with them
You're all too laser focused on Ruka age plus fact that we know her that you miss the point that her age barely enters the equation on Rin being a bitch who toys with people, she was just the new shiny toy and nothing else, if she was older their relationship would literally have played the same
Which is why I'll repeat once more, the manga is never framing it as the age gap being a issue but that Rin playing with people hearts being the issue
Really, just keep reading and you'll see how they will most likely never touch on the age gap aspect at all cause the mangaka is not thinking about it at any point
