In Another World With My Smartphone: Volume 6 by Patora Fuyuhara

16-year-old Mochizuki Touya continues everyday life in his new world, well aware that it could all come tumbling down at any moment. He's the budding administrator of Babylon, the fledgling grand duke of Brunhild, and now he's a... mecha pilot? Desperate to find a way to halt the incoming Phrase onslaught, Touya makes a mad dash for the Hangar of Babylon, hoping it can give him the edge he needs. What he finds is the Frame Gear, an ancient humanoid fighting machine! Join Touya and his ever-growing band of wives as they tap into their mechanical sides. All systems standby for a tale of swords, sorcery, and oversized wrenches.