The Hero Star-up Shard (or Universal Shard) is an item used to upgrade a hero's star level when you don't have enough of that hero's specific shards.
You can use a Universal Shard as a replacement for a hero's specific shards during star upgrades.

There are three types of Universal Shards:
-Rare Shard: used to upgrade the stars of Rare Heroes
-Epic Shard: used to upgrade the stars of Epic Heroes.
-Legendary Shard: used to upgrade the stars of Legendary Heroes

Note: Each shard type can only be used with heroes of the same category.