Rengoku no Trisagion

In the late 1800s, Thomas Alva Edison is a famous inventor, but he is also a master of fighting fallen angels who come into the human world. This role is called an 'exorcist' in the church, but Edison, with his new weapons, calls himself an 'artisan.' Levi is the son of a noble house, but when he is orphaned by an angel, he decides to follow Edison. Now he is Edison's apprentice, and does his best to make sure no one again has to suffer as he did.

(Source: MangaHelpers)