Helm Breaker AKA Kabutowari (兜割り, lit. "Helmet Splitter") in Japanese, is one of Vergil and Dante's command normal, based off of a move from the original Devil May Cry games where it is a standard falling air combo finisher. Originally in (Ultimate) Marvel vs. Capcom 3, Dante's Helm Breaker was a standard air combo finisher input.
Dante slams down his Rebellion while Vergil slams the Force Edge down to the ground in a slashing drop. This move can be substituted as a air combo finisher in Vergil's case in order to keep the foe to in place via a straight downward plummet for OTG followups, while for Dante it still sends diagonally-downward at an angle, forcing it to be more effective in the corner than in the open.