What if: Japanese retained the 9th division in Okinawa until April 1945.
https://en.wikipedia.org/wiki/9th_Division_(Imperial_Japanese_Army)
Background: Japanese on main Okinawa island had effectively 3 divisions (24th division full strength, 2 regiments of 62nd division, small elements of 28th division, 44th mixed independent brigade), reinforced by 5th artillery group (comprising ~120 field guns, 96 medium mortars, 54 ATGs, ~160 AA guns).
IOTL, in Battle of Okinawa US army had 101 thousand casualties (including psychiatric) of 183 thousands of initial invasion force.
Throw the 9th IJA division (by the way, elite one, unlike the troops defending Okinawa IOTL) in the mix, and the situation become quite contentious.
The answers to questions/plausibility comments are welcome:
1) Will the Okinawa invasion be cancelled in favour of some easier target?
2) Possible more successful Japanese counterattacks? Outright invasion failure?
3) Longer Japanese resistance extends into peak typhoon season of July-October, resulting in supply problems for US troops?
https://en.wikipedia.org/wiki/Typhoon#Frequency
4) Nuclear bomb used tactically on Okinawa (or other target?)instead of Hiroshima+Kitakyushu (rerouted to Nagasaki IOTL because of unexpected overcast) bombing?
5) Any other consequences?