Chikage

Martial Weapon (Longsword), Very Rare (Requires Attunement)

This old abandoned elven blade was once used by the knights of a long forgotten kingdom, who practiced the art of blood rites. Through ritualistic enchantments, they granted these blades a vampiric essence. When the intricate, rippled engraving that spans the Chikage's blade is imbued with blood, the sword sings in scarlet hues. However, the rite eats away at the wielder's very essence.

Magical. This longsword has a +2 to its attack and damage rolls, as well as having the Finesse property.

Scarlet Song. As a bonus action, you can expend up to 3 hit dice and sheathe your blade. The scabbard plunges scarlet fangs into your palm, draining you of your life essence, but coating the blade with a darkened ichor. For 1 minute, or until you shake off the blood as a bonus action, the Chikage deals an extra d6 of necrotic damage for every hit die you expended. However, at the start of each of your turns, you take necrotic damage equal to your proficiency bonus. This damage cannot be reduced in any way.

Corrupted Blood. When Scarlet Song is active and you hit a creature with this weapon, you can force them to make a DC 15 Constitution saving throw. On a failed save, a creature is poisoned for 1 minute. While poisoned in this way, a creature takes 1d10 necrotic damage at the start of each of its turns. A poisoned creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Hesitation is Defeat. As a reaction, you sheathe your blade and take an evasive stance, expending up to 3 hit dice to increase your AC by 2 per hit die against one melee attack that would hit you. You have to be able to see the attacker to do this. If the increase in AC causes the attack to miss, you can as part of the same reaction, make an attack against the attacker. If you hit, you deal an additional d6 of necrotic damage based on the number of hit dice expended.