Asato Tsuzuki (都筑 麻斗 Tsuzuki Asato), voiced by Dan Green (English), and Shinichiro Miki (Japanese), is the main protagonist of the story.
Tsuzuki has the appearance of an 18 year old man, though his actual age at death was 26. He has tawny brown hair kept above his shoulders and bangs that surpass his nose. His eyes are a vibrant purple color that are attributed to the supposed demon blood he possesses. Tsuzuki wears a casual black suit with a white button down under shirt. Usually he wears a large black trench coat that surpasses his knees over the suit. In The King of Swords he worked as a card dealer, in the casino area on the ship, where he wore his usual white button down with a black vest over it. In the St. Michael's storyline in volume 4, Tsuzuki was undercover as a priest at an all boy's catholic school, and wore a typical priest uniform complete with rosary. In volume 5, while trapped in the Count's storybook universe, Tsuzuki wore a plain white button-down, a long brown overcoat, and brown trousers tucked into shin-high boots.
He is notorious among his fellow Shinigami for his slacker qualities and voracious appetite for sweets such as cinnamon buns and cakes. His favorite color is light green, and he has a flower garden (in which he is known to have tulips and hydrangeas).
He was born in 1900, and was 26 years old when he died and became a Shinigami. He is 97 at the beginning of the first book and the oldest employee of the Shokan/Summons division besides Chief Konoe, and the lowest-paid, due to his perceived incompetence. It is revealed in the Last Waltz story line in volume 2 that he had a sister named Ruka who taught him how to dance and cook, though his skills in the latter are lacking. Ruka's name was revealed in volume 5. Her involvement in his past is left unclear and his parents are never mentioned, but when Muraki told Tsuzuki he has inhuman DNA, it's assumed that either his mother or father (or even both) is a demon, though it's uncertain if his sister had demon blood in her as well.
Though he is easily one of the most cheerful members of the cast, he hides a dark secret from his past. Both manga and anime reference terrible deeds he committed in life. It is suggested that Tsuzuki murdered many people, whether intentionally or not; this is brought to Tsuzuki's attention during his demonic possession by Sargantanas, a powerful demon who appears in the Devil's Trill arc. Doctor Muraki reveals to him from his grandfather's research that Tsuzuki was a patient of the elder Muraki for eight years and that Tsuzuki is, in fact, not quite human. During that time, he stayed alive without food, water, or sleep, and was incapable of dying from wounds, as shown by the many times he tried to commit suicide but failed but for one last time. Muraki suggested that Tsuzuki may possess demon blood [shown by the fact that he has purple eyes], and Tsuzuki found this incredibly hard to deal with. Whether one or both of his parents were demons is unknown, as is the humanity of his older sister; what happened to them during Tsuzuki's lifetime is also unknown, though it is implied in the St. Michael's arc that Tsuzuki had witnessed Ruka's death, and had felt responsible and helpless during it.
After his encounter with Muraki, Tsuzuki began to feel his suicidal tendencies come back ten times worse than when he was alive. When Muraki kidnapped him and took him to an underground lab to put his brother's soul in his body to kill him, Tsuzuki decided to set fire to the lab using Touda (an extremely powerful shikigami in Tsuzuki's ranks whose fire is strong enough to kill even a shinigami) to kill both himself and Muraki. Tsuzuki said that he was never supposed to exist in the first place for the suffering he went through and the people he had killed. But he was stopped by Hisoka, who begged him to live just for him and told Tsuzuki to be in his heart and his reason to live as he hugged him. Tsuzuki happily accepted this and embraced Hisoka as both were rescued from the fire via Tatsumi's shadow vacuum.
At the end of the final episode and the end of volume 8, it's revealed Muraki is still alive as Hisoka still has the marks of the curse Muraki placed on him. Tsuzuki returned to his normal self and both partners made a promise to stop Muraki together.
The first chapters of volume 9 deal with the aftermath of Kyoto, though this is unexplored in the anime. In volume 9, the Count hosts a costume party at the Hall of Candles, but loses his mask, which would render him visible if he couldn't find it. He hires the shinigami to help him find his mask. Tsuzuki wanders off on his own and the influence of the candles and the trauma from Kyoto manifest an illusion of Muraki, who threatens Tsuzuki, nearly causing another breakdown. Tsuzuki is saved by employees of the Security Division and subsequently comforted by the Count, who assures him that it's okay to still be hurt by what happened, and he's "only human."
- O-Fuda Magic
- 12 Shikigami
- High stamina
- Quick regenerative powers
Throughout the series, Tsuzuki develops an immediate closeness and affection to his current partner, Hisoka. He has a good friendship with Watari, and a sometimes strained relationship with Tatsumi, who had once been one of his partners. Tsuzuki gets along with most of the employees of Meifu, with the notable exceptions of Hakushaku, who constantly flirts with him, and Terazuma, with whom he has a fierce rivalry. Tsuzuki's relationship with Muraki is very tumultuous; although Tsuzuki hates him for his cruelty towards other people, Tsuzuki's desire to sacrifice himself rather than hurt anyone else prevents him from outright killing Muraki.