Meliodas and Elizabeth (The Seven Deadly Sins): Their relationship was creepy enough, with Meliodas' constant sexual harassment and Elizabeth's submissiveness to it, and no, her being the reincarnation of his dead girlfriend doesn't make it less creepy. It gets worse when we learn that Meliodas knew her since she was a baby.

Jacob and Reneesmee (Twilight): Jacob couldn't get with Bella, so he had to settle for her vampire baby. People defend that imprinting doesn't necessarily mean grooming, but it's still an option for them. Not beating the allegations was when Jacob was excited to learn that Reneesmee will physically be his age in a few days and will stop aging after that.

Sesshomaru and Rin (YashaHime): Their relationship was supposed to be paternal in the original, but Boruto: The InuYasha Edition decided that protagonists needed to be Sesshomaru's kids, and Rin was the only member of the opposite sex he spoke to out of filler episodes.