Can you use Not So Fast to counter an opponent's Heedless Resurrection?

Ruling: No. Not So Fast can only counter an enemy spell or ability that chooses a friendly unit or gear (one you control). When your opponent plays Heedless Resurrection, they choose a unit from their own trash, which is an enemy unit to you, not a friendly one.

Nuances:

• The spell must be both an enemy spell AND target your units/gear for Not So Fast to counter it.
• If you play Heedless Resurrection yourself, it is not an enemy spell and therefore also cannot be countered by your own Not So Fast.