A Gun in Another World

Sie Ryu and his classmates were having a peaceful school life, until a mysterious circle appeared and transported them into another world, normal people would freak out but Sie is not normal. Then they were given an enlightenment and given a choice to choose their weapon of their choice and Sie's classmates chose normal weapons, like swords, bows, spears, and their fists, but Sie chose the most obvious and logical weapon to anyone would choose if they got sent to another world.