He is voiced by Mitsuki Saiga in the Japanese version of the anime and Joel McDonald in the English version.
Yoite is tall in height, and slender in weight for his age. He has a ghostly pale complexion, though that can be attributed to his poor health, and his hands, feet, and torso are scorched black due to his Kira abuse (he wears beige gloves over his hands to hide it). His hair is jet black, and his eyes are a rich blue color. He often dons a beige cap over his hair, usually giving him the appearance of bangs falling over his face, though his hair is naturally middle parted. he wears a light beige turtleneck sweater (later shown to hide a scar over his jugular), and a long black trench coat reaching below mid-thigh. Because of Kira, Yoite occasionally goes blind, when that happens, his eyes glass over and become paler in color.
When he was younger, he was significantly shorter, but still very slender. He had worn the same hat and similar attire.
At first glance, Yoite is extremely antisocial and cold, preferring to not make conversation or show any genuine human emotion. He also has a bias towards not being in public, shown in both the anime and manga when Miharu crosses him, by chance, hiding between the cracks of two buildings off of a busy street. He was even worse when he was younger, as when Yukimi became his guardian, it took a long time for him to so much as speak, only doing so when Yukimi gave him his name.
As a wielder of the Kira technique, Yoite is a ruthless killer; he has no problem with brutally killing people who get in his way, even when they have nothing to do with the mission at hand, and even implies that he's not above killing children. This nature causes him to be dubbed the "Angel of Death" by multiple characters, though he was referred to as that long before he mastered the Kira technique. He is highly pessimistic, as shown by his desire for Miharu to make it so he never existed, as he doesn't wish for there to be a trace of him left. He is shown to dislike it when people take what they have for granted, as he has nothing going for him except his wish, with it being the only reason he's survived as long as he has.
Initially, Yoite rejects any compassion or care that others extend to him, as he feels he's undeserving of it. This of course also goes to show he lacks, or is completely absent of self-confidence. With enough perseverance, however, he eventually accepts the love and compassion others give him, and even will reciprocate, shown when he graciously kisses Miharu's forehead, alongside the various times the two have embraced. He also willingly allows Hanabusa to take care of him when his health has intervals of depleting, when he realizes that she looks out for him because she genuinely cares about him. His personality overall is very similar to Miharu's, to the point that the latter considers him to be "another [him]".
At first, Yoite doesn't seem to be bothered by using Kira, or whom it's used on. However, when Miharu becomes a staple in his life, he becomes much more hesitant to use it, because he wants to make sure he stays alive before Miharu could grant his wish. He also becomes more compassionate, realising people shared his same fear of death, eventually becoming full of grief over the lives he's taken. Yoite is described to also be highly intelligent, having an above-average IQ since he was young. Hattori also remarks how he was able to learn the required skills to join the Nabari world in merely a year, as well as learning the Kira technique.