The Year of Our War — Steph Swainston

Unique among his fellow immortals and mortal folk alike, Jant Comet can fly. His talent is a gift and a curse that has earned him a place in the Castle Circle as Messenger to the Emperor San--soaring high and free above the bloody battlefields of his world, carrying word back to his master of progress and regress in the ever-escalating conflict between man and the awful armies of giant, flesh-devouring insects.

But while Jant's duty is to remain neutral in the petty squabbles and power plays of the fifty who will neither age nor die naturally, bitter rivalries that have festered for centuries now threaten to incite a savage civil war. And Jant may be the only being alive capable of stemming the onrushing tide of destruction and the unstoppable insect infestation. For only he can gain entrance--through extreme doses of the narcotic that owns his soul--into a place of darkest wonders and revelations; a strange and horrific alternate reality that none but Jant Comet believes exists.