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

Also known as: When a Gun Nerd Is Reincarnated to a World of Magic · He Established a Harem army with 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！？