If he died by the god’s mistake, he was thrown into another world with a cheat gun is a Manga/Manhwa/Manhua in english language, Adventure series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

Tomoya Sadoshima died after a serious accident after returning to a convenience store. Then, after regaining consciousness in a pure white world, a woman of divine beauty emerged, she introduces herself as "The Goddess of Creation." The goddess of creation prepared a remedy for her suffering, she offers him to reincarnate a different world than his own. But it was a world in a war situation with the demon king. Begins; a story of Tomoya and his adventure to defeat the demon king and get the harem he so desires