Akaiye, Sword of the Elements

Formed when the four elemental blades are brought together, Akaiye embodies The Elemental Plane's fury and power in a weapon. It appears as a simple iron sword until you choose an alignment. Akaiye means "Primeval" in Elvish.

You have a +3 bonus to attack and damage rolls made with this magic longsword.

Elemental Bane. Any elemental damage caused by this weapon on an Elemental type creature ignores resistance and treats immunity as resistance.

Elemental Alignment. Each day at dawn, you gain 3 charges and may expend 1 charge to attune this weapon to one element of your choosing. You can do this a maximum of 1 time per hour. When you do, select from the following:

• Element of Fire: While attuned to the element of fire, this longsword changes to a volcanic stone with magma flying from the blade whenever it strikes, causing an additional 1d8 fire damage. You can use a bonus action to cause the blade to flare. All creatures within 10ft of you must make a DC 14 Constitution Saving Throw or be blinded till the end of your next turn. You gain resistance to cold damage.
• Element of Ice: While attuned to the element of ice, this longsword hardens into a crystalline frozen blade. The first time a creature is hit with this weapon, a small amount of ice coats its armor, clothes, or hide. On subsequent turns, you may use a bonus action to force the creature to make a DC 19 Constitution Saving Throw or deal 2d6 piercing damage. You gain resistance to fire damage.
• Element of Air: While attuned to the element of air, the air around this longsword swirls like a hurricane. When an enemy is hit by this weapon, you may force that creature to move 20ft backwards from you. The creature must succeed on a DC 15 Dexterity saving throw or be knocked prone when it lands. You gain resistance to force damage.
• Element of Earth: While attuned to the element of earth, this longsword appears to be made of obsidian and becomes impossibly sharp. Rolling a 19 on attack rolls is treated as a critical hit. When you land a critical hit on a creature, the ground underneath them pulls them down and their speed is reduced to 0ft for 1d4 rounds. You gain resistance to thunder damage.

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, Versatile, Sap