One time, when Seto was working in his office, there was a tap on his shoulder. It was Mokuba, who wanted to use his newly-acquired book called Demonic Rituals 101 to summon Succubus so he could finally get some tail. Seto decided to accept on the sole condition that it would be a three-way orgy between himself, Succubus, and Mokuba.
When he summoned it, something went horribly wrong; they had summoned an Incubus, which made Mokuba pregnant. The birth of the babies summoned the grandparents and their grandparent's parents. And their grandparent's grandparents parents. The cycle kept going on because demons are immortal.
It wasn't long before KaibaCorp had become a giant whore house. Seto eventually decided to turn it into a brothel and make twice as much money as he did before. Because Kaiba Brothers Brothel Corp. was becoming so popular, the building made all of Domino City into one big Red Light District. Nobody was without sex, and everyone was happy. This meant that there was no crime, and prostitution could finally be legalized.
When Siegfried caught wind of this, he sacrificed his manhood for a Kappa. Unfortunately his manhood was only two inches long, so he had to sacrifice some of his internal organs as well. This didn't quite work out, so he died from internal bleeding just minutes before his Kappa arrived via Hell's Bells Delivery Service. Pegasus on the other hand, was much more successful. He sold Cecilia's soul and turned Industrial Illusions into a factory for virtual girlfriends. He would no longer have to worry about his sexual urges that inspired him to kidnap Mokuba.
Domino City was filled with so much sex that it would never have to worry about anyone becoming an outcast from receiving syphilis or HIV. Everyone had an STD in some form or another; even the Blue Eyes White Dragon statues, which now lay in the cum dumpsters of the city trash disposal.
Noah Kaiba was so horrified at what he saw that he ordered another missle attack because if he couldn't have sex, neither could anybody else. After the missle "accidentally" hit Noah's computer thanks to Marik's hax0ring, Noah went to heaven and became a god.
When Seto finally died of AIDS at the tender age of 23, Mokuba decided that there was too much sex and invented Catholicism, as well as the idea that being gay was a mental illness that gave people STDs. He went on to become the first pope and began on his missionary quest. The demons were turned into holy saints, and regained their virginity. Then the power of Greyskull allowed Mokuba to grow a two-foot long dick, which he used to play Find the Strudel with Rebecca.
Noah saw this and smited Mokuba. Everyone's memory was erased so nobody could remember that fantastic orgy they had last night, except for Zorc Necrophiliac who was too busy digging up graves and having sex with the bodies to care.
The End