I suggest implementing an exchange system that allows players to trade surplus hero souls for a "Hero Soul Stone."
Proposed Exchange Rates:
5 SSR Hero Souls ➔ 1 SSR Soul Stone
5 SSR+ Hero Souls ➔ 1 SSR+ Soul Stone
5 USSR Hero Souls ➔ 1 USSR Soul Stone
Implementation Ideas:
Universal Soul Stones: Create a generic stone that can be used for any hero of that tier.
Weekly Exchange Shop: Introduce a shop with a rotating inventory that refreshes every week, allowing players to purchase Soul Stones for specific heroes.