Isekai Shokan Ojisan No Ju Muso Life Sabage Suki Salary Man Ha Kaisha Owari Ni Isekai He Chokuki Suru is a Manga/Manhwa/Manhua in english language, MONSTERS series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

The middle-aged man and airsoft enthusiast Daisuke Koga is summoned to a different world on his 40th birthday. Given the ability to turn airsoft guns into real guns, Daisuke must save the other world while traveling back and forth between reality and the fantasy world. Alongside female swordsman Rena, Daisuke becomes the only gun user and dominates in the fantasy world after work!