Soulbrand is a Unique Chest Armor in Diablo IV Season 15 for All classes. It comes from General Unique Pool - every Lair Boss (Initiate, Greater, Exalted, Belial) can drop it in addition to their dedicated table (one guide's Boss Loot Table Cheat Sheet).
Unique power
Your Healing Potions grant a Barrier for 100% of your Maximum Life for 1 second.You gain [25 - 30]% Damage Reduction while you have a Barrier and may drink your Healing Potion while at full Life.
Affixes
Primary Core Stat
Armor
Where it drops
General Unique Pool - every Lair Boss (Initiate, Greater, Exalted, Belial) can drop it in addition to their dedicated table (one guide's Boss Loot Table Cheat Sheet)