Slime Fantasy: The Search For The Lost Sword
What if you lost your life, only to be reborn in a new world? Many anime of the isekai genre answer that question, and one of the most optimistic ones is That Time I Got Reincarnated as a Slime. In this show, a salaryman is reborn as a blue slime critter...packed with magical power and positive thinking! He quickly unites the races of this new fantasy world to forge a peaceful and highly diverse new kingdom.
Slime Fantasy: the search for the lost sword
Fanworks In A Special Kind Of Magic, Naofumi explicitly uses his knowledge of his homeworld to create these, by first copying Captain America's shield (and giving Sam a good scare while doing so), and then gaining Raphtalia a sword with the same powers as Mjolnir!
Child of the Storm sets up Ván, the legendary sword of Frey, as this - forged of uru and vibranium, with all kinds of magic poured into it, it was capable of countering and absorbing Phoenix Fire. Unfortunately, a) since it was a literal last resort, there was never any time to record how it was made, let alone replicate it, b) despite people having searched for a million years, no one's ever been able to actually find the damn thing - something not helped by the fact that it has the most Boring, but Practical design imaginable.