Operation Downfall was the clusterfuck to end all clusterfucks. Even Operation Unthinkable pales in comparison to this.
Also, about that kamikaze force, the US Navy already planned for it by sending a decoy force that looked exactly like the invasion force but the main difference is that these ships would be loaded not with troops but with every AA gun they could strap onto them. This force's main purpose is to basically draw out as much of the kamikaze force as possible and shoot them down. Not to mention that by this time the USN was deploying as many 3"/50cal Mk 27/33/34 guns (which were specifically designed for this sort of thing) they could in preparation for this as well, alongside as many Fletchers and Gearings getting VT fuses for their 5"/38cal guns... then there is the Des Moines being deployed to the operation too and that thing is a floating air denial system back then. Not only that, but the USN -in preparation for this- deployed every carrier they could for the operation and loaded them with as many fighters as they could...
A good plan, but the Japanese wouldn't have gone for it. Their tactic was not to go for the USN fleet at sea, or even the carriers, they were going to wait until the US landing force had anchored in the bay and was deploying soldiers to the beach. The target of the Kamikazes were the troop ships which were far less defended than true warships and their goal was to inflict as many casualties as possible in an effort to shake US public morale. The Kamikazes were I think only going to be sent in a day or two after the landings began when the US had decided there was no serious opposition.
The US was firmly committed and did expect massive losses, but there are limits. The plan for Coronet depended on using the same troop ships as Olympic so every ship lost to Kamikazes is a delay to Coronet as the vessel is replaced. Lose too many and resupplying troops already ashore becomes a big problem.
The USN was also planning on leaving only escort carriers in the area, the fleet carriers and battleships were tasked to continue attacking infrastructure as they had been doing earlier leaving a very weak CAP over the landing zones, they just didn't expect any meaningful air attacks as US intel underestimated both the numbers, skill and fuel reserves of the Japanese.
There was also a huge problem with the VT fuses and that was that they were configured to engage the all metal IJN combat aircraft whereas in this battle they would be facing training aircraft which were mainly wood. Because they had less metal they had less of a radar return which spoofed the VT fuses causing them to detonate too late and miss the target. The Navy quickly identified this and began manufacturing more sensitive fuses but they weren't due to be ready in numbers until well after Olympic.
Additionally these Kamikaze weren't the barely trained waves of previous attacks but would be led by the instructors instead. These fellows had a massive advantage and that was the ability to fly at night. Almost all kamikazes were daylight attacks as the novice pilots couldn't navigate at night but the instructors could. They would also of course use the hilly terrain to mask their approach.
So what do we have? A massive night attack led by skilled pilots using terrain to evade radar attacking targets the USN didn't expect in numbers not believed to be possible. The two best defences, VT fuses and an aggressive CAP, aren't going to be available as the US main forces is ranging up and down the coast and not massed enough to meet this attack. And once the troop ships are crippled you have a vast number of experienced Japanese soldiers including the core of the Kwantung army and all the remaining tanks poised to counter attack against the troops already on the beaches. They would also have no doubt sent in the last of their real pilots including several legendary aces to engage US aircraft first, though the night kamikaze attack would probably have been an OCP.
The key to this entire plan was good intel, and the US had absolutely terrible intel. They vastly underestimated Japanese air power and concluded that even if they did have aircraft they had no fuel for them because they failed to spot the last oil tanker which miraculously avoided the US subs and brought enough fuel for the big kamikaze run. The US fleet would have continued aggressively bombing Japan but in doing so would have sailed away from the invasion beaches leaving only support ships to defend the transports which were stationary, hampered by terrain and filled with bodies. We know from Okinawa what happens when Kamikazes use terrain to avoid detection and it isn't good. Their target wasn't the carriers as the USN expected and were going to use as bait, but instead just to take as many lives as possible.
It wasn't until post war that the US investigated Japanese war records and found exactly what they were up against. The US planned for six million casualties with at least a million dead for these two operations and that was without knowing the full extent of Japanese defences.