Shido Takamiya Itsuka is the older brother to Mana Takamiya and his foster sister Kotori Itsuka, and is the protagonist of The Bond of Souls. It is implied that he is the reincarnation of Yuri Volte Hyuga, a powerful Harmonixer who was given the moniker "God-Slayer".
Due to his amnesia, Shido remembers very little of his life, other than knowing that he was adopted by the Itsuka family and somehow knew that his foster sister Kotori was a Spirit, however he cannot recall the reasons why, and anything past five years ago is a blank. However, since he lost his memory, he has been having a reoccuring dream in which he stands in a graveyard with seven graves, six each bearing strange symbols with the seventh has the name "Yuri Hyuga" written. His meeting with the Spirit Tohka and his involvement with the organization Ratatoskr has raised several questions about Shido's past, especially about his abilities as a Harmonixer and the power to seal away a Spirit's power.
Shido, on more than one occasion, has been thought to be the reincarnation of a Harmonixer granted the title of "God-Slayer", due to the fact that he had defeated a God himself, and further hinting this is the dreams involving him and a girl named Alice Elliot, who always calls him Yuri rather than Shido is a spirit
Shido is usually and passive about most things while annoyed with his sister's antics, however he cares deeply for his friends, right to the point where he would risk his life for them. However, when he met Tohka, who was a being known as a Spirit, he wondered why it was that Spirits cause Spacequakes whenever they appear, and upon learning that he has the ability to seal away a Spirit's power, he resolved to save them.
However, when he discovered that he couldn't just seal them, but also merge with them, Shido began to question if he was human or not, and always asked himself why he had this power. He also feels strange attachments to a girl in his dreams, who he seems to remember.
Depending on what Fusion Shido is in, his personality shifts. However, his most prominent Fusion, Amon, seems to be the only one where Shido's original personality remains intact, however he is extremely violent towards those that would harm his friends, and on more than occasion nearly killed the aggressors, much to his horror.
Despite his fear of using Amon's power, he won't hesitate to use it whenever his friends are in danger. He is deeply infatuated with Tohka, Kurumi, and Origami, three of many girls he has come to love and care for. However, out of all of them, he cares for Tohka the most, and strives to do whatever he can to look after her, due to her lack of knowledge about the world.
Shido has been known to use two abilities so far.
For unknown reasons, Shido has the power to seal away the powers of Spirits, and even take on some of their own abilities. However, in order to seal away their powers, Shido has to make them fall in love with him, which is easier said than done, as each girl has a different personality. Another troublesome thing is that, to completely seal away a Spirit's power, Shido has to kiss them on the lips, much to Tohka's chagrin.
While initially unaware of his heritage, Shido is one of the few humans capable of merging with supernatural beings such as Spirits, Demons, Angels, and the likes. However, the traditional method for fusion is that a Harmonixer must kill a monster, and then merge with its soul to attain greater power, whilst running the risk of becoming a monster themselves. However, Shido's method of Fusion is very different: he merges with the power of the Spirit's that he has sealed. However, if a Spirit suffers from negative emotions and enters an Inversed Form, Shido's fusion is also affected to a great degree.
Chernobog (The Everlasting Darkness): The first fusion Shido gained, and the embodiment of Tohka's powers. While in this state, Shido can use all of Tohka's former abilities, and even adopts a male version of her look. His personality is somewhat similar to hers when she first met him during her battle with the AST, however Shido has put Tohka's safety above all others. While Tohka is in her Inversed Form, Chernobog adopts a more twisted appearance, however he still wishes to protect Tohka: only this time, he's willing to kill anyone that stands in her way.
Egil (The Lonely Glacier): Described by Kotori as the Fusion version of Yoshinon, and the embodiment of Yoshino's powers. While in this state, Shido can move at high speeds, leaving behind a trail of ice wherever he goes, and can even create ice blasts, pathways, walls, and vice versa. His personality is just like Yoshinon, and is very attached to Yoshino, placing her needs above all others and will do anything to protect her... even if it meant attacking his friends. Whenever Yoshino is in her Inversed Form, Egil becomes beastial, and attacks anyone in sight, seeing everyone as an enemy. However, for some reason, he seems to be afraid of Yoshino.
Efreet (The Eternal Flame): A personafied warmonger and the embodiment of Kotori's powers. In this form, Shido loves the thrill of battle and will do everything it takes to keep it going, even giving himself a handi-cap to make things interesting. Similar to Kenpachi Zaraki of Bleach, Efreet purposely holds back and rarely ever goes all out. Shido is capable of controlling any flames that sprout from his body, and wields a sword made of everlasting hellfire. While Kotori is in her Inversed Form, Efreet's body becomes encased in flames, and has but one desire: to burn the world to its very foundations.
Incubus (The Immortal Earth): One of the more powerful fusions at Shido's disposal, and the embodiment of Kurumi's powers. While in this state, Shido's personality is just like Kurumi's, and doesn't seem to hold human life in high regard, claiming it can be replaced. It is apparent that, whenever using Incubus' abilities, Shido's timelimit in Fusion form is decreased. Incubus, true to his name, is something of a pervert, and has tried on more than one occasion to seduce the girls, especially Kurumi. Shido's powers while Kurumi is in her Inversed Form is currently unknown.
Lancelot (The Undying Light): The embodiment of Origami's powers, as well as the definition of chivalry. In this form, Shido is very hostile towards other Spirits besides Origami, and has sworn absolute loyalty to her, desiring nothing more than to spend an eternity with her. His shield is capable of repelling a Spacequake, while the sword can easily cut through an Astral Dress. Whenever Origami is in her Inversed Form, Lancelot goes berserk and attaks any Spirit he can find, including Origami herself. It's also noteworthy that, because of its hostility towards Spirits, Shido rarely uses this Fusion.
Amon (The Void of Destruction): Out of all the fusions in Shido's arsenal, Amon is easily the most powerful, as well as the most terrifying. Shido's personality remains intact, however when enraged, his anger is magnified times ten, and has, and more than one occasion, nearly killed someone that has threatened his loved ones. Shido is downright horrified by this, and only uses Amon whenever he truly needs it. Because this Fusion does not require Shido merging with the powers of a Spirit he he has sealed, Amon is not affected when his respective Spirit enters their Inversed Form. According to Roger, Amon is known as the Master of Absolute Destruction.
??? (The Ultimate Being): Though Shido has little memory of ever using this Fusion, it is, to his understanding, the most powerful Fusion that he possesses. From what he remembers, he used this fusion five years ago, possibly shortly before he lost his memory, and though not much about it has been revealed, Roger has stated that this fusion is easily the most destructive. He also mentioned it before, saying that Shido was the second person to successfully merge with this being. The name of this being is lost to Shido, but it is implied that is either the Seraphic Radiance, a being that is capable of killing a God, or the Dark Seraphim, the Seraphic Radiance reborn.
- Shido's method of fusion is similar to Shania of From the New World. Upon reaching a holy ground, Shania would form a pact with the holy ground's respective spirit and borrowed their power, thus granting her a new form. Shido, in a sense, formes a "pact" with the power of the Spirits he has sealed.
- Ever since Shido awakened to his powers as a Harmonixer, his hair has slowly become darker, changing from blue to reddish brown.
- Shido appears to have picked up a few of Yuri's habits. He gets along well with dogs (a reference to how Yuri viewed Blanca as a dear friend), has begun using vulgar language, and, for some reason, he apparently has the same motion sickness Yuri has whenver he's on a boat.