The EPIC Storm is a pure storm-combo mirror-style matchup where the faster, more resilient combo wins, so Force of Negation lets us counter their Tendrils of Agony or an enabling spell like Burning Wish for free on their turn. Dauthi Voidwalker exiles cards that would go to their graveyard, disrupting Echo of Eons' flashback and any graveyard recursion, while applying pressure if the game goes long. Fatal Push, Street Wraith, and Voice of Victory are all low-impact against a deck with almost no creatures to kill (just a couple of Hexing Squelchers and a Runehorn Hellkite) and no real attackers to punish, so they come out for proactive disruption. Be aware that Veil of Summer, which they play in their main deck, makes their spells uncounterable for the turn and gives them hexproof from blue and black, so it blunts Force of Negation just as it blunts black discard like Thoughtseize. Hexing Squelcher also makes their spells uncounterable while it is on the battlefield. Counters are therefore not a safer plan than removal or discard here; try to act when they are tapped out of Veil mana, and remember Veil itself is a noncreature spell that Force of Negation can hit.