Ronin Blade

Weapon, rare (requires attunement)

The length of this undecorated katana (longsword) is dotted with pits and marks, and its sharp edge is lined by a permanent, dark crimson stain. You gain a +1 bonus to attack and damage rolls made with this magic weapon. The blade grows stronger when you face multiple opponents. When you threaten at least 2 opponents that your allies do not, you gain advantage to attacks made against those creatures.

As the one attuned, once per day, whenever you would be reduced to 0 hit points, you instead have 1 hit point.