I've been playing around on my alt "rawsause w eggos" with a koraidon balance team, and I feel like if you want to run koraidon, then you should definitely look into covert cloak scream tail! I feel like when it comes to the past vs future paradox wars, scream tail with an investment to get the protosynthesis speed boost serves to be the perfect past paradox to change the future of the battle. With access to misty terrain, you can shut down not only electric terrain removing the quark drive boosts from them, but also severely reduce the power of miraidon's draco meteor allowing koraidon to better combat them, and misty terrain helps check those who runs psyspam cores with indeedee + armarouge/hatterene. Scream tail also has other very neat utility moves such as dual screens to beef up the team, fake tears for your special attackers like flutter mane or sandy shocks, howl to further boost koraidon's attack stat, trick room for speed control, and even perish song as a means to safely win the endgame if having the pokemon advantage or to pair up with gothitelle for a perish trap core.
The set I'm currently using is protect, play rough (single target fairy move to hit miraidon harder and snipe tatsugiris), perish song, and misty terrain, and it has been the mvp of my koraidon team!