Warnings: Incest, Dark, possible dub-con, possible non-con,

Genetic Sexual Attraction: The phenomenon of sexual attraction between close relatives, such as siblings, first and second cousins or a parent and offspring, who first meet as adults.

Ben/Kylo and Rey are sibling or cousins that for whatever reason do not find out about each other until they are adults. Ben falls in love with her but she doesn't reciprocate, not in that way and his unrequited love takes him to some dark places.