Root & Earth - The Chronicles of Mori, #1

Kaito Rin can move faster than an arrow in flight. As a veilwalker of the Village of Root and Earth, he's just one of many warriors with an extraordinary ability or 'trait', equal parts spy, assassin and errand boy. When a routine patrol sees him bested by an injured woman, he's both intrigued by her skill and appalled by the danger she represents. Itami is the sole survivor of a devastating attack that massacred her village, and she might have led the danger to Kaito's doorstep.
Because threats new and old are rising out in the deep forests, ones that will cut close to the bone for the people of Root. Whilst Itami seeks vengeance and Kaito's own student struggles with a terrifying new trait, schemes are being unfolded that will lay bare past secrets - and, if Kaito can't stop them, wreak a horrifying future.