Kuro travels back in time to 6:24 PM (relative to Hawaii) and then teleports to where aqua is.
Kuro then rips a hole in space and records aqua's solo, and then travels back to the original dimension at the time right after the fortress was created.
After that, Kuro plays the previously recorded solo, melting aqua's face and claiming the fortress-hill in the name of KURO!!!
My Fortress Hill.