Sword Brothers
From the Castlevania Wiki, the Castlevania wiki
Sword Brothers is a spell in Symphony of the Night that is performed by Alucard's Sword Familiar (while it is being used as a Familiar, not equipped in the Hand). It is the only Spell that is accomplished by a Familiar in this game. The Sword Brothers spell is accomplished by pressing down, then rolling the directional pad 180 degrees forwards and holding it for a while once it reaches up, and then suddenly press down and attack at the same time. The sword will perform a move that damages all enemies on the screen. This will consume a heafty 30 MP, the second highest consuming spell after the Soul Steal.
