The single edged blade of this weapon seems to be made of pure obsidian with a slight blue hue to it. Thought to have been wielded by an entity named Odin.

Dormant

This longsword grants the following benefits in its dormant state:

• You gain a +2 bonus to attack and damage rolls made with this magic weapon due to this weapons exceptional craftsmanship and sharpness,  and it deals an extra 1d6 slashing damage to any target it hits.
• While holding the longsword, you can use an action to cast the following spells from it: darkvision and darkness from it, Once a spell has been cast using the longsword, that spell can’t be cast from the longsword again until the next dawn.

Awakened

When this longsword reaches an awakened state, it gains the following properties:

• This weapon seeps with darkness turning the extra slashing damage into force damage and increasing its effects to 1d8 extra damage to any target it hits.
• As a reaction when you are targeted by a spell or ranged attack that succeeds in hitting you, you can make a contested melee attack against the spell or ranged attack with Zantetsuken, if you meet or exceed the opposing roll you take no damage cutting the intended spell or ranged attack in half. You can use this property once per combat.
• Add Banishment (DC15) to the list of spells that can be cast from the longsword.

Exalted

When this longsword reaches an exalted state, it gains the following properties:

• You gain a +3 bonus to attack and damage rolls made with this magic weapon. In addition, the weapon ignores resistance to slashing damage.
• When you attack a creature that has at least one head with this weapon and roll a 20 on the attack roll, you cut off one of the creature's heads. The creature dies if it can't survive without the lost head. A creature is immune to this effect if it is immune to slashing damage, doesn't have or need a head, has legendary actions, or the GM decides that the creature is too big for its head to be cut off with this weapon. Such a creature instead takes an extra 6d8 slashing damage from the hit.
• Add plane shift to the list of spells that can be cast from the longsword.
• The saving throw DC for spells cast from this weapon increases to 17.

Proficiency with a Longsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Magic, Damage, Combat, Versatile, Sap