The Inkhorn is a special implement used to write names into the Book of Life and the Book of Death.
Story[]
God's Inkhorn is first mentioned in Chapter 4, on an inscription in The Old City stating the Inkhorn will only reveal itself once the Book of Life and Book of Death are present; however, Neon White and Neon Yellow do not understand at the time, and are intercepted by Neon Green before they can.
White largely ignores the Inkhorn until Chapter 11, when Mikey informs him that it is needed to unite the Book of Life and Book of Death, and bring God back into Heaven as a result.
He and Neon Red find it at the Coliseum at the Glass Port in Chapter 12, where Red sacrifices herself to allow White to be the one to unite the books and stop Neon Green; White finds the Inkhorn in God's other hand, though Green is there too, also intending to unite the books to rule over Heaven.
A final duel takes place between White and Green, and White wins. He is given a choice: use the Inkhorn to write Green's name into the Book of Life, or the Book of Death. Either way, he faints afterwards - as the Inkhorn is not meant to be used by mortals.
History[]
During the Ten Days of Judgement, the Inkhorn is what God would use to write the names of sinners into either the Book of Life or the Book of Death.
God kept the Inkhorn after being overthrown by the Believers - it was last seen in His hand at the Coliseum, which could not be opened by Believers, Angels and Neons alike.