so i heard you like spirit weapons
At the edge of anyone's memory, there was a fight between the Titans of the world, ravaging the planet and returning it to the oceans. One of them, Valkyrie, ended up victorious, and stabbed her sword into the seabeds of the nascent world, forming new landmasses for the people and creatures of the world.
Several centuries ago, the technology of soulsmithing was invented by the (center of Valkyrie kingdom I have yet to name). Soulsmithing is the process by which one can imbue an object with a spirit, giving it life and magic. This gave them and those that they gave the technology distinct advantages in combat, resulting in many of the kingdoms of old being replaced, such as the Northern Crown, who was conquered by the Sunbacked Wing, only for the resultant merger to be unstable, ending in revolution that broke up the Sunbacked Wing state.
Spirit weapons come in many different forms. For example, the Northern Crown's legendary sword Corazon, the ancient scythe Marzi, and the giant shield Mallow. They have the soulsmithing in common, however - all spirit weapons, regardless of type, have a spirit within them that can appear and that imbues the blade with magical powers. Creating spirit weapons requires special mana crystals found most readily in (center of Valkyrie kingdom), which is why they have stood the test of time and survive to the present.