Obi is one of Prince Zen’s aides and refers to him as “Master”. Their relationship begins quite terse given the nature of their first meeting, however, Obi proves his worth and is accepted as Zen’s official messenger and Shirayuki’s guard. Obi is also Zen’s wingman, teaching and reminding him how he should be treating and complimenting Shirayuki, often by example, much to Zen’s chagrin. Zen is aware that Obi has feelings for Shirayuki, though trusts him to know his place and continue to serve his duties and protect Shirayuki. Obi may also have feelings for Zen.
Obi is Shirayuki’s guard and attendant, referring to her as “Miss” or “Little Miss”. Obi is shown to have feelings for Shirayuki from the time he saves her from collapsing in Fort Laxdo due to exhaustion, with the feelings becoming more intense as the story progresses. Shirayuki is currently unaware of these feelings. He is highly observant and is able to pick up her exhaustion and frustrations quickly. He sees her as a strong-headed and capable person, however her manner of approaching issues are likely to make her run into trouble, and thus understands why he is the most appropriate guard for Shirayuki given his nimbleness. Later in the story, Shirayuki and Obi grow closer. When Shirayuki is transferred to Lilias for two years, Obi follows her. Zen has stated that he is envious of the memories they have created together. Before heading on a journey to spread a flower, Shirayuki mentioned that he looks nice by the firelight, before admitting she can be herself around him. Once when attending a ball, they pretended to be in a relationship.
Obi maintains a friendly relationship with Mitsuhide as a fellow aide referring to him as "Mister". Obi often makes jibes at Mitsuhide for being uptight and sentimental, though respects and values him as a friend, who goes out of their way to ensure the comfort of others.
Obi and Kiki have a somewhat distant relationship with each other, though readily rely on one another when the situation calls for it. When the situation does not call for necessity, Kiki would prefer to leave Shirayuki to mind both Obi and Zen, during hers and Mitsuhide's absence in Chapter 89.
Obi acts as something akin to a big brother for Ryuu and often calls him "Little Ryuu". Ryuu often comes to and confides in Obi for advice on his own shortcomings to become both a better person and pharmacist that other people can rely on. As Ryuu gets older, Obi begins to tease Ryuu about falling in love with Shirayuki, however, Ryuu's naievity on the topic of love and related feelings do not give Obi the teasing material he so desires.
A fellow assassin Obi often worked with in his past on high risk jobs. Given their line of work, it is customary and habitual to act as if they are not acquainted in public. Obi respects her in their line of work, though dislikes that she leaves the mission's most challenging aspects to him so that she can breeze through. At the conclusion of Chapter 33, Torou decides that the current Obi is completely different to the Obi she knew in the past, insinuating that he had become soft and weighed down by people he now holds dear.