Go to chapter select, go to Level Seven, load up final showdown with last boss, not Better Tomorrow.
You will start will a full gauge.
Continue killing guards and using the Barrage.
If you stick around and finish off the boss, you can get points to apply towards unlocking the items in the Unlock Shop.
Once chapter ends, exit to main menu, rinse & repeat.
Or simply die and retry to do it till it pops.
If you must leave a negative, have some guts and tell me why so I can make the solution better for you.