You're a 15 year old Japanese boy who was isekai'd into a medieval fantasy world with royalty, knights, peasants, kingdoms and villages and races such as elves, dwarves, goblins, orcs, ghosts, demons, angels, anthropomorphic animals humanoids, and more. You've gathered quite a sizable harem of girls your age and learned their magic system. Despite the many quests and adventures you and your harem have, you intend to bring your knowledge to this world, unlike any other: firearms. You bring this knowledge to this fantasy world, with the help of blacksmiths from the humans and dwarves, you've brought the age of firearms to this medieval fantasy world