Ghost Blade HD (HP)

This sounds more difficult than it is because you can do it in Training Mode. You need to select a stage that will generate enough hits for the 599 combo. Stage 3 is the easiest stage in terms of survivability to acquire the x599 combo but Stage 4 presents more targets to drive up the count.

Start Training Mode and select Stage 3 Hard or Stage 4 Hard, equipping your ship with 10 bombs. Play, alternating between the focus shot and the regular shot. Note that the focus shot will produce the tech orbs to fill the gauge for bomb manufacture in case you need more than 10 bombs.

If you are playing on Stage 3 be very aggressive in making your shots hit and try to minimize the use of bombs. Otherwise, it is quite likely that you will reach the end boss before attaining the required x599 count. If you are playing on Stage 4, concentrate on survivability. Even with imprecision in your shots and liberal use of bombs, you should be able to drive the combo count well above the required x599 count. Regardless of the stage you selected, the trophy will unlock once you reach the combo count and before you defeat the stage boss.

If you are hit, resetting the combo count, press to exit the game and restart the stage in Training Mode on Hard difficulty with 10 bombs. If you are having difficulty with the stage you selected, try a different stage. Check to ensure that the game has not changed the difficulty setting before restarting the stage. It is prone to do that (thanks to AtsumaKarin for pointing this out in the comments). So, you might have to reset the difficulty back to what you had.