
Did I assume you were American? I believe I asked the person whom you are calling an enabler. Do not misconstrue my words I am honestly curious as to what country this person lives in. Never did I say grooming or pedophilia was a good thing. What is a child in certain countries is an adult in others. For example, in Sudan girls can marry at the age of 10. Does this make it right no. This is a cultural thing. Which is why I was curious where he/she was from.

I don't think you're a pedophile for thinking this is normal because perhaps you've just grown up in a place where this is considered normal.
However, it isn't. 12 and 17 are vastly different ages and there's no way these two could be on a remotely similar maturity level. 12 is pre puberty, 17 is almost out of school.
Also, I don't blame your sister in the slightest, she was just a child. Her boyfriend though is the weird one and lowkey a pedophile and groomer. To even consider a 12 year old girl to date when you're 17 is insane to me. It's just predatory. There's no way it can be healthy, sorry, even if it may look like that on the outside.
Gloriousking etc was a bit rude with how they said it but they cited scientific proof made by professionals that these predatory age gaps are not healthy. They never said they were the professional, but what other professionals say on this topic and that isn't in your favor.
Also... it's a bit contradictory that you say "this is just fiction" in one sentence and then you bring up your real sister in the next.
A 17 year old shouldn't date a 12 year old. Period.
But genuine question, if you are in Yuu-nii's position, how do you properly reject this child's advances and make him properly understand the difference of their "likes"?