Mana Bank

When you cast a spell or put an ability on the stack (other than this one), you may pay {1}. If you do, put a storage counter on Mana Bank.
Tap fortified land, {x}: Put X storage counters on Mana Bank.
Tap fortified land, remove X storage counters from Mana Bank: Add {x} to your mana pool.
Remove 3 storage counters from Mana Bank: Mana Bank is indestructible until the beginning of your next upkeep step.
Fortify - Remove 2 storage counters from Mana Bank.