My first Final Denouement comes from two commonly used tropes that seem to perplex people to no end. What is the dual appeal and popularity of childhood friends and incestuous siblings to Japan? I propose that while these are hardly the same fetish they both tap into a very similar cultural desire. This makes them oh-so-popular with the Japanese but very odd to the Western audiences.
Japanese society promotes a very formal culture. There can be countless barriers between casually meeting people let alone dating. How many times in anime and manga have you seen people be reluctant to use someone else’s first name despite having know them for the longest time? A recent Anime 3000 podcast makes it clear that while they are opportunities and venues to get to know people better in Japan, overall the Japanese tend to value and protect their privacy from strangers. These barriers are not strictly Japanese, it is just that they can be stronger and more culturally enforced in Japan.
Opportunities to circumvent these barriers are especially appealing to the socially awkward. A way to instantly have a connection to someone without having to go through the complicated social dance could be extremely appealing to someone who has two left feet with such matters. It would be an ideal dream to know someone that would let you bypass these social barriers. To be instantly on an informal level with someone that would easily promote a more intimate relationship is the magical appeal of the childhood friend or the sibling.
The childhood friend is a person you have know all your life therefore you can instantly talk to them as an equal. The childhood friend is known before the tricky politics of gender relationships have formed in your head. Before the wall that separates men and women has become concrete. So when both friends awaken to sexuality there is this open bond that formed naturally without any of the messy complications of adult relationships. The sibling exists in an even more familiar and barrier free existence. Incest also has the added taboo factor which might turn away some but actually attract others.
These two factors then become understandably attractive. The socially inept do not have to change who they are or attack a seemingly unbeatable foe. They just have to be themselves and can still connect with someone romantically. This is not totally running into a realm of fantasy but it is a wish for a simple answer to a more complex problem. I would equate it with wishing to win the lottery. Fun to think about but horrible to put any amount of concrete hope into.