The Lines of Sanzu are a special trait of a Shinigami. Represented by three lines around the head, it is the place where a Shinigami manifests its power of the Madness of Order. How much it surrounds the head is dependent on a Shinigami's age, as in the case of Death the Kid, who has his lines covering only the left side of his hair. It has been shown that only one shinigami with all three lines connected can exist at a time.
The Lines of Sanzu seem to be directly linked to the Shinigami's own natural special abilities, as Kid was able to access some of his father's heightened abilities after connecting one line.
There is also a direct connection to Shinigami himself, as he displays visible signs of pain after Kid connects his first Line. Spirit Albarn's worry suggests that the connection of the lines - while technically beneficial to Kid - does not bode well for Shinigami. Shinigami, however, sees the lines advancement as progress for his son.
During the operation to infiltrate Baba Yaga Castle, Kid immediately concludes that his father gave him Brew because of the power of the Lines of Sanzu and resolves to meet (what he sees as) his father's expectations. Curiously, he shows no prior knowledge of the Lines' significance, while reacting very quickly to the changes they temporarily brought about.
During his battle on the Moon against Asura, when Kid connected all three Lines of Sanzu, Death was killed in the process, crumbling into dust and "absorbed" by Kid, according to Excalibur.. Kid also learned the true power of a Shinigami, which was to utilize the Madness of order and turn people into mindless puppets. Yet, as Kid finally realized how much power his father possessed, yet never saw his father use such power, Kid realized Death had faith in humanity, hence he would have faith as well and resist using such Madness.
- In Japanese Buddhism, the Sanzu River is the River of Three Crossings and the way to the afterlife. It is the Japanese equivalent of the River Styx. A person's soul crosses from the land of the living to the land of the dead by crossing one of three ways, depending on the weight of their sins, or karma: the good cross a bridge, the neither good nor bad cross through a shallows, and the bad cross through deep waters where vicious snakes swim.
- In the Anime, all three Lines of Sanzu are connected by Kid, which turn Liz and Patty's Death Cannon forms into enormous, golden cannons called the Sanzu Death Cannon. The attack from a single shot from this cannon had the ability to destroy Asura's monstrous form.
- It is possible that, since Kid was born from a fragment of Shinigami's soul, this means they both share one "pool" of power.
- When connected, the Lines of Sanzu resemble a halo, emphasizing how a shinigami is an "Angel of Death."
- In both endings of the anime and manga, when Kid activates all three Lines of Sanzu, it leaves multiple cracks in Shinigami's mask when Kid battles Asura.
- However in the anime, Death does not die after Kid activates all three Lines of Sanzu.