Nineball is really solid, you definitely have to keep proper footsies against him. Once you have him on the defensive, you can actually win though. He is a patient blocker but he is a bit weak to grabs, especially simple grab set ups surprisingly. Honestly, try not to fear him too much, it's how I started taking a lot of games from him. He is still a player that'll DP in expected moments, get hit by overheads, etc. You just have to get momentum and switch up your approach a lot, so that he isn't punishing you and getting his Ragna time on.
I wish I was better at explaining so sorry if I sound stupid. Most importantly, just remember Nineball isn't unbeatable, nobody is.