Gun-Ota ga Mahou Sekai ni Tensei shitara, Gendai Heiki de Guntai Harem wo Tsukucchaimashita!?  

When a Gun-Nerd Is Reincarnated to a World of Magic, He Established a Harem Army of Modern Weapons!?, 軍オタが魔法世界に転生したら、現代兵器で軍隊ハーレムを作っちゃいました!?, He Established a Harem army with Modern Weapons!?, กันโอตะได้กลับชาติมาเกิดใหม่ในโลกที่มีเวทมนตร์เลยสร้างกองกำลังฮาเร็มพกอาวุธปืนที่ทันสมัยขึ้นมา!?

Youta Hotta was 27 years old, a virgin, high school dropout and former hikikomori. Despite facing difficulties throughout his life since high school, he met an untimely end when he got stabbed to death on the way home from work at a metalworking factory. However, it appears that Youta has been reincarnated in a fantasy world now.