How to get an insanely high number of combo hits:
1. Play through the game once while keeping Noire at her initial level (Lv. 5) and get the True Ending. Make sure to pick up the Twin Bangle in Virtua Forest.
2. Start a New Game+ and play until you reach the White Heart battle on chapter 3.
3. Initiate the battle and defend until White Heart stops attacking.
4. Spam X.
5. End the battle when you have reached the desired number of hits. For perfect game purposes it is not necessary to get any higher then 99999, since that is the cap in the Play Data section.
Noire's highest STR during the battle is 84, which is not enough to do any damage even though she has the Ignore Enemy Traits ability and White Heart is under Guard Break. Noire has 227 STR at level 5. With STR bonuses from hits (Until You Cry), she gets an additional 137 STR. There are three Processor Parts that lower STR with a total of 40. On top of that there is the Twin Bangle which lowers STR with 240.
I have no idea what causes White Heart to stop attacking and start defending. It could be that she is out of SP and have no regular attack to use instead.
No DLC was used.
The time needed for 100K hits is approximately 7 hours.
The attacks used was Break Crush (Break Attack, 3 hits) and Paralyze Fencer (EX Finish, 3 hits).