It was never stated that Shishui has a cool down time.
He is the original owner after all.
If it did, please post the scan.
The mere fact that KA has a cooldown at all is proof that Shisui himself would have a cooldown time after using it. No one has ever stated that it being used by someone other than its original owner is the reason for the cooldown time. And we know for a fact that no such cooldown exists for any other MS jutsu when that jutsu is used by someone other than its original owner (Kakashi and Madara with Kamui, for e.g). In fact,
the only thing that has been stated to reduce KA's cooldown time is Hashirama's cells, so I am not going to assume that the cooldown time magically disappears with Shisui when there's nothing that even hints at it.
It's quite the opposite really
It was never shown with limitations
Dat no-limits fallacy. Not to mention that's not correct anyways. KA still possesses limitations, such as the need to have eye contact, the long cooldown time, and the inability to spam it due to said cooldown time.
Danzo did it in the summit with no eye contact from a few meter distance towards mifune.
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. It would have been a small issue to slightly raise his bandages and cast KA.
Itachi used KA on Kabuto to break his Edo tensei control over him, in a cave parts uknown.
That is not true at all. Itachi's MS brought out the crow from Naruto's mouth, and then the crow cast KA on Itachi, which is why Itachi himself says "
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", and "
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". Kabuto was never subjected to KA.
