Attaining a SSS rating may seem daunting, but there is actually an exploit you can use to get the score. What you want to do is load up the first level on hard difficulty. It will also help if you build high chains during each wave to get a higher score. Make sure along the way you buy the micro impulse gun. I also suggest you buy the grenade gun for tight situations. Make your way wave after wave to the boss fight. It's a giant witch. Don't make it about killing her though. During the battle bring her down to 1 health. (as revealed in the sky) Every now and again she will make little big witch clones that spawn a TON of enemies. The trick here is to survive and kill anything that moves, except of course the big witch. Through my own personal experience, I hit 490,000 points and then killed the witch. This gave me a SSS rating. My accuracy wasn't great at about 65 percent but i still hit the SSS. Getting this trophy unlocks all lower grade trophies as well.