Yuuji is kind person who puts others before himself. This often draws much confusion and annoyance from Shana, as prior torches from Shana’s experience exhibited selfish attitudes. However, Yuuji’s compassion and empathy sow the seeds of attraction between him and Shana. He accepts his fate with no ill feelings, a trait which surprised the Flame-Haired Burning-Eyed Hunter, knowing that most Torches would be depressed to the point that they would even commit suicide before their existence wears off. In fact, Yuuji uses this fate to commit acts of heroism, defended by the belief that even if his existence would one day disappear, his sacrifice would be proof that he had once lived.
Despite all these changes, he still struggles to live the ordinary life he once had and at the same time, trying to help Shana in her battles and save Misaki City and its inhabitants.
Crimson Lord, Human Contracted to: Snake of the Festival
Shana and Kazumi, who both harboured feelings for Yuuji, both decided to write him a letter, and whomever he would respond to would be the one he had chosen. Unfortunately, he had disappeared on Christmas Eve, and everyone except those who had knowledge of who he really is, had forgotten about him.
It is later revealed that Yuuji chose Shana over Kazumi. He was even surprised that his feelings were already there for a long time and contemplated about all the time wasted with her. With this realization, he made a decision and voluntarily erased his existence on Christmas Eve, for the sake of changing Shana’s fate.
Meanwhile, he also received advice from a mysterious voice which offered him the chance of saving Shana from the endless conflict between Flame Haze and the Crimson Realm. Yuuji accepts this offer and merges with the owner of the voice; none other than the Crimson God, “Snake of the Festival.“Employing his new powers which even exceed that of a Crimson Lord, Yuuji joins Bal Masqué, where the Priestess (Hecate), the Strategist (Bel Peol) and Fecor (Bel Peol’s right-hand man) accept him as the new leader. After, he goes to Misaki City and faces off with Shana, defeating her, and proceeds to the Yoda Department Store, where Eita and Kazumi are, to claim the Haridan which belongs to Bal Masque. Kazumi asks why he returned the letters she wrote to him and Yuuji replies that he cannot think of anything to say to her that won’t hurt her feelings (meaning Yuuji returned Kazumi’s letters instead of bluntly rejecting her, thinking that his actions would be less hurtful than saying it openly. This indicates that he has chosen Shana over her.).After encountering and defeating Shana in Misaki City, Yuuji restrains her powers using the Tartaros and takes her away to the Seireiden. He and a few member of Bal Masqué then travel to the rift between the human world and the Crimson Realm, the place where the body of the Snake of the Festival is sealed.
Bal Masque successfully awakens the Snake of the Festival’s true form, which brings forth an advantage in the war against the Flame Haze. The Snake’s true form is successfully brought upon the Earth which gives enough of a morale boost to Bal Masque’s troops that the Flame Haze begin losing the war. Sakai Yuuji announced his plan to the retreating Flame Hazes that as the God of Desire, he wishes to create a new world, one that fulfils every Denizen’s wishes that there is no war, an abundance of Power of Existence, and no pain and suffering like this world, named Xanadu. Furthermore, he added that Flame Haze should not oppose this as this also indirectly fufils Flame Hazes purpose that no more Denizens would kill humans indiscriminately for Power of Existence. However, the announcement has a darker purpose. Most of the Flame Haze made pacts with Crimson Lords for revenge, injustice, and suffering. Now with the weight of protecting a new world being irrelevant to them, is too cruel, most mentally broke down, leading to a massacre by Bal Masque’s troops. After the war, he reveals the location that is appropriate for the creation of Xanadu, Misaki City. However, Johann was awakened by Pheles after Kazumi summoned her to the battlefield because of Sydonay weapon almost killed her when he used it strengthen the tower before Khamsin destroys it. He take out the Reiji Maigo from Yuuji but Yuuji won’t allow him take it away from him. Yuuji asked him the reason and intention of him taking away the Reiji Maigo. He immediately answered that he doesn’t agree with Yuuji’s plan after Xanadu is created and after the God of Creation is separated from him. He also noted that Yuuji had belittles love. He said that Yuuji had underestimated Shana’s feelings for him. He pointed out that Yuuji thinks that Yuuji himself is the only one who could sacrifice the world for love, when in fact, he himself had done the same thing. When Pheles asked him to leave the battlefield, he immediately released the Reiji Maigo and hugs Pheles. Later, Johann and Pheles cast a spell to summon a van which appears to be Gyuuki in a form of a van to take Yoshida and the two of them away.
Through various battles and tactical planning, he successfully created Xanadu by sacrificing Priestess as the beginning of the creation of the new world. However, Shana and her team returns to fight Sakai Yuuji as they realize the mirrored world would cause imbalance of Power of Existence in the far distant future if Denizens consumes Power of Existence recklessly. Through ensuing battles, Shana and Margery Daw successfully reconstructed the Restriction Spell to include a Law that humans can never be consumed in Xanadu. This is a last ditch effort as Shana’s team is too small to prevent the creation of Xanadu, so they merely wanted to protect the Xanadu humans instead. As they feel relieved that their plan worked, Shana is agitated to see Sakai Yuuji smiling.
Sakai Yuuji, foreseeing this plan reveals that the whole Restriction Spell is a secondary effect. In reality, the only requirement is to wait till midnight so that Reiji Maigo will refill, during which time he asks the Professor to place a special Restriction Spell to obtain extremely vast amount of Power of Existence under his control, where he can direct it to the creation of Xanadu and null the Law placed by Shana. Shana and the other Flame Haze have not been beaten, but have clearly lost and can only watch helplessly on at the creation of Xanadu. However Sakai Yuuji, as the Snake of the Festival, hears the Denizen’s, as well as the Flame Haze’s, wish and does not undo the law put in place by Shana.
As the Denizens leave to Xanadu, Sakai Yuuji parted with Snake of the Festival. The Strategist, holding the essence of God of Desire gave him a chain-shape key to Tartaros. At the end, the God of Desire stated he grew fond of Sakai Yuuji, a mere torch that was willing to allow himself to be used as a tool to fulfil his plan, and even if nobody else approved of his plan, the God of Desire approved it and gives his blessings to Sakai Yuuji, as they departed to Xanadu.
Later the Spiral Organ appeared, gave Yuuji a crystal containing Unrestricted Spell for bringing back the lost things, grant basic protection for his body and embedding a new unrestricted spell into the anti-flame ring Azure, saying it’s been wonderful working with Sakai Yuuji. Later, Lamies left a last parting gift, naming Yuuji’s new Unrestricted Spell, Grammatica and ask him to contemplate on the meaning of it.
Now, fully himself, he decided to face Shana and Margery Daw in the final battle, and Sydonay impressed by the boy’s action decided to ally with him and fights Margery Daw. During the battle Sakai Yuuji activated the green crystal and cast it on Yoshida Kazumi, with the last plea for her to agree. The spell activates and it restored all the destruction caused at Misaki City and healed damaged people although he regretted that dead people cannot be revived.
Shana asked Sakai Yuuji what is his intention and he replied that in order to atone the killing of Flame Hazes and Humans on his quest, he will travel to Xanadu that has no Misaki City alone to teach Denizens and humans to coexist peacefully, even if it takes thousands of years so that he can finally be together with Shana without guilt. Shana punches Yuuji and gives him Hirai’s Torch.
Shana and Alastor was furious with his philosophy of severe self-punishment. They used their tremendous strength to overpowered Sakai Yuuji and leads to his defeat. In the limbo, Johann confronts him smiling and teases Sakai Yuuji that he underestimated the power of love again. He awakens, carried by Shana shyly said he just need to ask and she would go with him to Xanadu together without a thought. Admitting his loss he replied to Shana, he ask for her forgiveness, ask her to be with him in Xanadu and she accepts happily.
As they embraced and kissed, the Spiral Organ Unrestricted Spell activated and Sakai Yuuji becomes a “solid existence,” as prophesied by God of Punishment—something more than a normal torch or a Mystes. As Sakai Yuuji and Shana delights at this revelation, they departed to Xanadu.