3D Dot Game Heroes

King Block is located in a cave east of the Castle in area E2 (you must grapple east-to-west across a river to reach him). He sells a variety of swords in exchange for Small Blocks. Buy any sword from him to unlock the trophy. Note that swords do not carry over between playthroughs, but Small Blocks do. Wait until the playthrough where you are attempting to acquire every sword before you purchase any swords from King Block. Alternatively, you can save your game before buying a sword, buy one to unlock the trophy, then reload your game.

As of the online update 1.01, swords that you purchase from King Block do carry over to subsequent playthroughs.