What is the true identity of the Demon King Priest and the Heroic Girl Yusiris?

Having many identities may be due to his reincarnation (it is not very clear in the book, but it should be very close). In his previous life, he was one of the seven demon kings, Mephistopheles. The most elusive of the seven demon kings, the demon king who controls the power of the soul has mastered soul knowledge that is higher than that of the Supreme God, and has the terrifying power to ignore the opponent's defense and directly destroy the soul. He is good at cheating on the balance of fate to achieve effects that his strength cannot achieve. The soul is immortal, and the body can be resurrected no matter how it dies. It is known as an existence of "absolute immortality". He likes to play pranks everywhere, and is filled from head to toe with bad substances. He takes pleasure in watching other people make jokes. Good at distorting the so-called reality. Everything he said could be true, but when combined it turned out to be an outright lie. Adhering to the principle that "the best lie is not to lie, but to let the other party make the wrong judgment", he has been called the Great Liar in all the worlds that have existed.

The father of Rose Girl, the believer of the Silver Wolf Clan, and the maker of all D-version bridal outfits. He has left many traces and emotional debts in this world. I don’t know whether it’s because of the irrecoverable damage caused by the death blow of the Supreme God, or because of the limitations of the current world, or simply because I don’t want to be responsible for my feelings. Every time for some reason, all my power and memory are lost, and I return. Infant state to achieve the purpose of 'final disappearance'. He has been reincarnated three times, and Ulysses is his current reincarnation. Although he ran away once more in OTL to save Rasha, he became the current Jusis because of his own desire.

At present, his identities include Mephisto, Mephis, Mephi, Ulysses and Usis...