After Tails was adopted by Myotismon and Xion, he met Cosmo, the girl of his dreams, on the set of Sonic X. When Cosmo was killed off of the show in the last episode, Tails wenht inot a deep depresion. In order to stop his son's torment, Myotismon used his powers to bring Cosmo back and had her and Taiols betrothed to be married when they became of age. Tails returned the favor by taking the position as heir to the leadership of The Court of Demons, even though he had declined several times.
After a few years, Myotismon started to feel guilty about adopting Tails without the blessing of his real parents. So, he had his uncle, Dr. Facilier, conduct a seance to get that blessing. The spirits of the two tailed prince's true flesh and blood appeared succesfuly and told Mytoismon and Xion that they would give their blessing only if Myotismon were to promise to treat Tails as if he were his own flesh and blood and to never give up on him, no matter what happens. Myotismon and Xion agreed to this, saying that they had already done that so far and that it would make no sense to stop now.