Gunslinger weaver in another world

In a fantasy world where magic is everything, Kaen is sent into this world with none. Labelled as useless in society ruled by mana, he survives from using weapons and knowledge of another world. Guns require no spells, no mana , no divine law or approval. As his "mana-less" killings spread fear across kingdoms, mages fail to counter him and even the kings begin to take notice. Hunted,exploited and feared, this gunslinger must choose if he is just a tool of war... or a calamity that shatters a world built on magic