The Grim Reaper and an Argent Cavalier

The Grim Reaper and an Argent Cavalier (死神と銀の騎士, Shinigami to Gin no Kishi) is a manga written and illustrated by Irono.

Plot
In order to attain immortality, the Grim Reaper began devouring the souls of people. To gather more souls, he created the Larvae and unleashed them upon the world.

Cyan is a former member of the Argent Cavaliers, an order of holy knights dedicated to eradicating Larvae and founded by the Grim Reaper's sister, Lemuria. Cyan left the Argent Cavaliers in order to hunt down the Grim Reaper with Jade, a descendant of Lemuria, and put an end to the Larvae threat once and for all.