User blog comment:DivaytFyr/Yet just another speculation/@comment-4207271-20130516230838/@comment-9631479-20130517124133

Thank you, Sicarius001, for reminding me of spiritual beings' breathing. This would mean that underwater breathing in Ichigo's Inner world was not just for style, afterall!

(P.S. This theory is almost nothing compared to the great work called "The inherited will - One Piece". If you are fond of this manga, I highly recommend you to check it, it is truly worthy.)