Evolving Weapons

In the long line of Bjernson's, at least three of them have claimed to wield their signature family weapon, "Bjern's Brightblade". The unusual aspect here is that each time the Brightblade appeared as a different weapon; initially a short sword, then a massive greatsword and finally the glaive from the tale of Bjern the Blasphemer.
That's the way with bards and legends though, you're never sure what's actual magic and what's just the magic found in a good mug of ale.

Evolving Weapons

Far from a simple bard's tale, scholars have confirmed the existence of at least a small number of enchanted weapons capable of unlocking new forms and greater power under the right circumstances. Borrowing a term from the study of fiends, sages have termed these to be "evolving weapons", in that they undergo a metamorphosis without any particular spell or other ritual being performed on them.
Those few that have been identified by scholars have all been ancient items from the early to mid-Olmec era based on their design. It is not believed that any modern mage is capable of generating magical items of this type or potency, especially since the destruction of the Mana Forge in Wave Echo Cave.

Known Examples

Redacted -

Mechanics & Inner Workings

How each weapon evolves is unique to the creation and purpose of that item. Some are said to devour the essence of particular foes, while other legends report that the weapon matured in time with the wielder.

Significance

Great historical value, and potential martial value if unlocked.

Rarity

Exceedingly Rare