Is this Aizen before or after his fusion with his Zanpakuto?
Actually, don’t bother answering that, because either way he wins. His Hypnosis is way more potent than any genjutsu in the Narutoverse excluding Infinite Tsukuyomi and it activates the moment someone gazes at his Shikai release.
Besides he’s a spirit. Shisui even sensing, perceiving, and fighting him is a near-impossibility