Takashirou Giou

"'Wounds made by a friend will never heal...'"Takashiro Giou (祇王 天白 Giou Takashiro) is the current head of the Giou Clan and is one millennia old, having never been able to die or be reborn like his fellow Zielit Guardians.

A suave and charming, but at the same time no-nonsense man who regards sacrifices as a necessity, even if it breaks his heart to be so cruel. Possessing an ancient grimmore, the  Spellbook of Solomon, he is a powerful magician who can cast the strongest of spells and call forth the wildest of monsters when the situation calls for it – even if he only does it as a last resort when nothing else can be done.

He first introduces himself as Yuki’s older half-brother and tells him he’s spent years looking for Yuki. Even if Yuki is reluctant at first, he eventually joins his brother in the war.

It is revealed in Story 23 in the manga that he is not truly Yuki's elder brother and he apologies for manipulating and lying to him but Yuki forgives him, telling him that despite that, Takashiro is still very important to him.

Immortality/Longevity
Back when the war started, Takashiro cast a forbidden spell that sealed a Duras inside himself. Therefore, he is not reincarnated like the Zweilts; instead, the Duras keeps on regenerating his mind and body, meaning he will never age, die from physical wounds or forget anything, ever. It is shown that there are severe drawbacks from this and he has come close to losing his sanity numerous times.

Necromancer
Takashiro is a necromancer of unbelievable strength and knowledge and uses a grimoire, much like the reborn Reiga, the Book of Solomon. His magical aura red, in contrast with Reiga's bright blue.

History
Takashiro is first introduced as Yuki's older half-brother. When he meets Yuki for the first time, he tells him that he and his father had been looking for him ever since his birth fifteen years earlier. Although it is not yet revealed at the time, Takashiro seemed to be hiding something from Yuki. The truth being that he had performed a forbidden ritual that allowed him to take a Duras into his body. Because of this he, unlike the other Zweilt Guardians, has not been reincarnated. Instead, he has lived for a thousand years, remembering everything, including how the war with Duras first began. He also heals almost immediately after being injured. He is also the one responsible for continually causing Yuki and the Zwielt to reincarnate so they can continue fighting Reiga. He then apologizes for lying to Yuki, telling him that he is not really Yuki's brother, but Yuki forgives him, telling him that despite that, Takashiro is still very important to him.

Takashiro was born more than a thousand years ago during the Heian period and lived with the other Giou clan members in the mountains. Takashiro and Yomi were two of the only members who took a liking to the young Reiga and didn't judge him despite his family history. On the contrary the two always did what they could to take care of Reiga even though they knew his situation was fragile. As the three grew up their powers also evolved and they became part of the Four Saints, the leaders of the Giou clan. After an incident in the capital, the court summoned the clan to help purge a horde of Duras. Takashiro was sent with a couple of trained fighters while Yomi and Reiga were left to protect the village. Before leaving he had a talk with Yomi who expressed concern about Reiga, not because she feared him the way the other villagers did, but because she feared for him, feared he wouldn't know how to handle all the power he had been given. Unfortunately, this conversation was overheard by Reiga.

Though Takashiro manages to calm him, he still has to leave and the mission takes longer than he first figured. When he returned the Giou clan's village was awash in flames, Reiga had called a horde of demons and removed the village's barriers, leaving the people as a feast for the Duras. Searching for answers, Takashiro stumbled upon Yomi's body and Reiga bathed in blood, but as soon as he tried to talk to him, Reiga attacks, leaving Takashiro with his characteristic scar on his left cheek.

Since then Takashiro has blamed himself. He blamed himself for not being there for Reiga, for not saving the village, for not listening to Yomi when she said Reiga was dangerous. Thus the war began and Takashiro swore to see it through because he felt it was his responsibility, his mistakes which caused it. Through the generations he used the Lost Spell of the Giou's clan to seal a Dura in his body, keeping him alive and giving him extraordinary healing abilities. He took it upon himself to carry the weight of the Giou clan and all mankind, sharing it with no one, suffering in silence. Using ancient spells he called back the souls of dead clan members, reincarnating them in new bodies so that they might live to fight again. Abandoning human emotions was his only way to deal with what he had to put himself and others through to end the war. Upon meeting Yuki his emotions return and he finally opens up to tell the story, apologizing for what he put them through time and time again for his own selfish reasons.

Unknown Child
In Story 61, it is revealed that Yomi was pregnant with Takashiro's child. This pregnancy was kept a secret, known only to Reiga and Yomi.

But as was to be expected, her child grew fast during pregnancy and so did her belly, revealing the secret. It is not yet known why, but Yomi's pregnancy was not allowed and Takashiro was even ordered by the imperial court to kill her and the unborn child himself. Why? Who knows. However, he could not bring himself to do so.

The elders and Yomi's parents also were strongly against this, so the only person outside of this she could confide in about this subject was Reiga, whom she later asked to run away with the baby. But that's when the elders found out and when Reiga got to her on that night, it was too late, he found her dead body collapsed on the floor and her belly seemingly cut open.

Nothing more is known about the child, as it is not even certain whether the child was born before the elders killed Yomi or not.

The only clue about the child is something Yomi confides to Reiga, "This child is not a normal human."

Quotes

 * "I may not be your real brother…but for me you’re as important as family." (Speaking to Yuki.)
 * "You only worry about others and don’t care about yourself. Can’t you understand how we feel when we see you like this...?"