Board Thread:Questions and Answers/@comment-3459763-20140408035439/@comment-11051098-20140425001352

Xilinoc is right - Hollows in general consume souls in an attempt to fill the hole where their heart used to be, a void that can never be filled.

And Blazenite104 is right - only Adjuchas need to consume souls, to avoid reverting back into Gillians. If they do that, they're stuck and can never become Adjuchas again.