This becomes available once you complete the game.
It can be found in the gift shop and costs $10million.
It increases all your battle stats making those AAA ranks become that little bit easier to reach.
There are two quick ways to raise cash:
The fastest way I could find for this was to keep playing the "Weight limit" sub mission on Normal mode with the standard costume. DO NOT use a special costume as you will lose 95-99% of earnings per mission while using one (EG: "Ulti-Mondo).
Keep your combo meter up so your blood level stays high and spam the adrenalin burst (RT+X) attack for instant kills - this ensures the elevator continues to move upwards all the time.
You should get a minimum of $600,000 for about 1min10 or less (my personal best is 57seconds), or $1mil+ if you can manage to make it without being hit once.
It's a fairly hefty grind that will take several hours and hurt your fingers most likely, so don't waste your money on presents for the women until you hit the $100mil mark and pop this achievement - you really don't want to grind more than you need to!
An easier, but more time-consuming way to boost the cash would be Episode 1 on "Very Hard" with no upgraded costume. Just avoid all Tokio's bullets and you will make $500k in about 90seconds each time. You get a lot more money for being on the hardest setting so don't waste your time on anything lower.
(EDIT: Skip all the cut scenes for that speed, and install the game to reduce loading times if you can, will take a good 5mins per run if not)
1) As soon as it starts, hold left and get behind the dumpster
2) Once Tokio stops firing, move out and hug the right side (he will always shoot left, then run away).
3) Follow Tokio around the left corner, and stick to the left to get behind another dumpster.
4) Once Tokio stops firing, move to the right hand wall and then walk forwards to next dumpster (again, he will always shoot where you WERE, not are... so don't stay on the left!)
5) Wait for him to fire and then move diagonally forward and left towards far dumpster - if done correctly, Tokio will just run away and not fire another burst.
6) WAIT at the corner as he will shoot. As soon as he finishes, move to the far side (left wall) and get behind dumpster.
7) As soon as he turns and runs, move out and get behind next dumpster on the right.
8) Once he fires again, move out and to left side for final dumpster. Tokio will then run away for the final time - follow him and end the mission $500k richer for less than 60seconds of actual play
If anyone is able to make a video to show this, and you don't mind me adding it to the solution, please let me know - my instructions should hopefully be easy to understand, but videos definitely help!!!