Shido has the looks of a handsome young man in high school. He has straight blue hair and bands down to his neck and amber brown eyes. During the times where he borrows another Spirit's power, the color of his eyes turns into a more golden shade with dilated whitened pupils. He is often seen wearing the male Raizen High school uniform during his everyday life circumstances.
During the events of Miku Lily, Shido had to crossdress as a girl to interact with Miku, thereby disguising himself as his alternate identity, Shiori Itsuka (五河 士織?). During the time, he was seen with long blue hair, and he wore the standard female Raizen High School uniform. He also wore a flower hair clip as a hair accessory.
An average young man that originally had no interests in the opposite gender until he got forced to be by his little sister. He is now compelled to deal with females on a constant basis, something that he wasn't used to before.
Kotori described another interesting part of Shido's personality. As a result of being abandoned by his birth mother, Shido has become unusually sensitive to other people's despair. It is this empathizing nature that makes him regarded as the best person to handle the Spirits.
Shido is also a very kindhearted person that can sympathize with others. These traits are what caused most of the Spirits to fall in love with him, as the thing they seem to lack most of all has always been a person who could accept and understand them. Even Miku, who treated everyone like puppets, ended up changing her worldview because of him.
Shido also possesses a strong will and a genuine willingness to forgive others. He will press on to save the Spirits despite the great personal risk to himself. When responding to Natsumi's comment about the trouble she caused him, he compares her actions to what he went through during all of his past attempts to help Spirits and can only call her actions childish pranks: this is a girl who nearly ruined his reputation and erased all his friends and would've then erased him had she succeeded.
Despite his determination to save the Spirits, Shido's conviction has been shown to falter more than once. When he first learned of Kurumi's real, malicious nature, Shido was left scared and unsure on how to approach her, having become actively wary towards the "Worst Spirit". Similarly, after Mukuro outright rejected him and dismissed his beliefs as hypocrisy during their first conversation, Shido began to question if sealing the Spirits' powers may actually be a mistake; as doing so leaves them much weaker and more vulnerable to getting captured by DEM. During times like these, Shido has often needed the advice and emotional support of those closest to him to renew his resolve.
Shido was born in an attempt by Mio Takamiya to resurrect Shinji Takamiya after he was killed by DEM. By absorbing Shinji's corpse into her own body, Mio planned on reconstructing Shinji as well as bestowing him her powers to ensure that he could become her eternal lover. However, due to the fact that the human body is too frail to withstand Spirit powers, Mio only initially gave Shido one power: the power to gradually seal other powers into his body.
Shortly after he was born, Shido was abandoned by Mio and adopted into the Itsuka household at a young age. Five years ago, an incident caused Kotori to become a Spirit due to a misunderstanding on her part and was tricked into becoming one, but neither of them can remember anything about that incident until Kotori personally used her powers again five years later, which awakened those memories in both of them again. It was discovered that Shido possesses the ability to seal the powers of Spirits around the time Kotori became a Spirit, but how he got the ability in the first place remained unknown.