The Mechanical Halo is the prize offered to the fastest of the Assassins recruited to deal with the demon infestation in Heaven.
Purpose[]
Somehow, the Mechanical Halo allows its bearer to remain in Heaven for a year, as well as granting them "godlike" powers, until the next Ten Days of Judgement wherein they will have to compete again for a chance to keep the Halo. The chance to win it is the incentive offered to the Neon assassins to aid Heaven with its demon problem.
It is currently worn by Neon Green; it was forged in the Old City by the Believers, using a page from the Book of Death.
Neon Green wearing the Mechanical Halo.
It is revealed later by Neon Red that the Halo is more like a control device than anything, and keeps Green under the control of the Believers, while also causing him to become feral and bloodthirsty.