ISEKAI SHOUKAN OJISAN NO JUU MUSOU LIFE: SABAGE SUKI SALARYMAN WA KAISHA OWARI NI ISEKAI E CHOKKI SURU

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!

(Source: Houbunsha, translated)