A Wild Last Boss Appeared! (Yasei no Last Boss ga Arawareta)

From the introduction: Welcome to Midgard. Here you will find your standard isekai fantasy world, complete with swords, magic, demons and summoned Japanese teenagers. Well, maybe it is way too standard, to the point of coming out as a bit fake and bland at times. After all, its maker isn’t the brightest person, and she pretty much lifted a lot of inspiration from an Earth not too dissimilar to your own.