User blog comment:Omega natsu2/Chapter 364: Tartarus Arc, Part 1: Immorality and Sinners, Predictions./@comment-8153438-20131219131955/@comment-7418318-20131219161530

Maybe he just transformed his hand into a claw, like he did before and just ripped it through Brain with just his physical power.

Not everything needs to be a spell, just because it's in a magic world.