The comes in when once Matt realizes that he's slept with his sister, he wants to marry her and goes to a website to show that any children they might have would be normal! And once the ship has sailed, well, there's no calling it back to shore.
Ayumi's brother, Yuuji, is a definite siscon, and Koyoi Bessho is defined by her brother complex.
And Dana seems to be at least subconsciously aware of the connection on some level and is bothered by it.
Six years after authorities first uncovered Australia's most depraved child abuse case, Betty Colt, a court pseudonym, has shared photos on social media with the family motto plastered across the bottom.
As such, he's remarkably by Kanako's attempts at seduction.
Weirdly, they decide to stay together after the truth comes out, citing the fact that incest is fairly common in royal families.