R-Type Final 2 (JP)

To unlock the R-Typer 3 difficulty, you have to finish the game on R-Typer 2 difficulty, either by playing through the entire game or just completing any Stage 7.x on Score Attack.

Despite the description saying "cleared the final mission", you CANNOT get this just by playing a 7.x mission on Score Attack, you need to do a full playthrough.

R-Typer 3 is only a tiny bit more difficult than R-Typer 2 ... a few extra enemies, and slightly higher rate of enemy fire.

You can use as many credits as you need, but there are several checkpoints where, stripped of your power-ups, you'll have a really hard time progressing, so just focus and try really hard not to die at those bits.

EDIT: some info from AudibleJam509 ... "FYI, you can get these in score attack with stage edits. Also, these achievements do NOT stack meaning you’ll have to finish the game on R-Typer, R-Typer 2, then R-Typer 3 SEPARATELY."