He is voiced by Joji Nakata in the Japanese version and Jamieson Price in the English version, both of whom also voice the Count.
Sojiro is a middle-aged man with slicked-back dark hair, a receding hairline and gray eyes. He has a chinstrap beard with a goatee that flares out and wears glasses.
His usual outfit consists of a pale pink dress shirt with the sleeves rolled up, pale khakis held up with a white leather belt and white loafers. While working at Leblanc, he wears a black apron with a white pinstripe design on it and has his pants legs folded up to mid calf. During his off-time, he wears a white two-button blazer and while driving, he wears a white trilby with a red-white-and-blue striped hat band.
Sojiro is serious and a bit cold to the protagonist in the beginning, begrudgingly taking him in as a favour to a friend. Like many characters in the beginning of the story, he is cautious of him due to his probation, even stating that he will do very little if the protagonist gets himself into trouble. He is a rather cynical person, warning the protagonist that he should be careful who his friends are and chastising him for getting involved in the affairs of others, even if he was trying to do the right thing. However, Sojiro seems to have a soft spot for cats, as he instantly changed his mind about throwing Morgana out of the house, after hearing him mew, claiming that he was just too damn cute. He also made him something to eat right away, despite claiming that feeding him was the protagonist's responsibility.
However, as the protagonist continues to live with him, Sojiro slowly builds trust in him, allowing him to go outside during nighttime, first around the area then anywhere around Tokyo, and even beginning to teach him to make Leblanc's signature coffee and curry. He also begins to joke around with the protagonist more, seeing that the protagonist is not the delinquent that his probation makes him seem like. Eventually, he opens up to him about his past with Wakaba Isshiki and her daughter, Futaba, up to and including why he took in the latter after the former's death.
Sojiro is a very smooth talker and often charms women with choice words, stating that he was "quite the ladies man" in his youth. He takes an immediate liking to Ann, commenting on her kindness and even asking if she has a boyfriend. Despite this, Sojiro has never been married and has only truly loved one person ever: Wakaba. Wakaba's "suicide" became one of his biggest regrets in his life, due to the fact that he took her warning that she may die soon as a joke. It is also part of the reason why he adopted her daughter, Futaba, though he considers this a selfish reason since it's just his way of atonement. Despite the life she lives as a shut-in, he allows her to do so knowing that her mother's death haunts her and to atone for doing nothing even after Wakaba foresaw her impending death. At times, he wonders if he really is the best person to raise her.
After the protagonist helps Futaba to leave the Sakura residence and learning of both of their involvement in the Phantom Thieves, he begins to stand up for the protagonist and becomes supportive of their efforts due to their goal of taking down Shido, a man responsible for Wakaba's death. Once he finds out that the protagonist and Futaba (along with all their other friends) are part of the Phantom Thieves, he accepts it and promises to keep their secret, despite them being some of the most wanted people in Japan at that point. This is largely due to the fact that he always suspected that there was something more behind Wakaba's death, but kept his nose down because he didn't have any real evidence.