Bluesteel Blasphemer: Volume 1

Yukinari Amano loves guns. After reincarnating into another world, the young man goes on a journey with Dasa, the younger sister of the girl who gave him a second life. However, while on the road, the pair are attacked by a local deity--an "erdgod." No normal person could possibly defeat one--so when Yukinari uses his knowledge of guns and newfound abilities to do the impossible, he becomes worshipped as the area's new god himself!