User blog comment:Godisme/Everything But The Rain Op. 3 Dark of the Moon/@comment-2182964-20130315151041

It is known that Isshin encountered an imperfect Arrancar roughly 20 years before the start of the series. It's quite possible this "Hollow" is that imperfect Arrancar, meaning Isshin using the FGT is looking likely. Brilliant chapter though. Kubo's def. bringing his A-game this time.