Alright, here's mine. got it from a dream, so it is still very rough.
RENEGADE
the main protagonist is a potentiate for the world's greatest fighter(he can use whatever weps you choose at the beginning of the game- a primary wep and helper wep {such as a longsword and 3 shortswords or a scythe and a gauntlet. you can instantaneously switch by using magic.}) (the world is covered in demons and monsters and what have you.) One day, as he comes home, he notices many monsters grouped. he starts getting nervous, 'cause monsters only group in large numbers for blood and death. the monsters turn to face him, badass cutscene battle, then more monsters come in and you (the player) take the fight with prime and sec. wep combos, and if you are really good, wep switch combos. (scythe hooks onto enemy, brings it in, gauntlet spears monster, flings it up into the air, time slows down and you switch weps to dual pistols, keep him floating on a cloud of bullets and shoot him full of more holes than swiss cheese, for instance.) the more of these you do, the more points you get towards mastery of weps and skills. the protagonist runs into the house and finds his sister dead. he sees a man standing over her, who vanishes into thin air. flashbacks to when his sister put a seal on him to maintain his insane power. back to reality, the seal breaks now that the sister is dead. you lose control of the main character, who is 100x stronger and is insane. he is now powerful enough to kill with his bare hands, which are cloaked in shadows. he can use the shadows to form weps, or use them as a ground ripping, air splitting pulse of energy. (think grand king cero + visored getsuga tenshou.) later in the game, he also gets control of chaos and void(which is how you wep switch). however, to stop him from being an unstoppable badass, a sanity meter in the bottom of the screen (Much like tome of darkness) starts to deplete. when the bar is gone, you go from full control of character, to no control, he kills everyone, & game over.
the army thinks he killed his sister to unleash his power! not taking any chances, the army sends everything they have after him. after regaining his sanity, and 50 burning tanks later, he gets away and sneaks into a hi-tech school of warfare, where he sees the principal. the principal is the man who killed his sister! so he's gotta make friends and become popular, so that he can't be taken out. however, just like at any other school, there are kids who object to this. also, the principal is gonna try to kill you to cover up. you gotta think! every choice you make affects you. you gotta stay alive. i might put in a moral choice, but i doubt it would work well. you are basically evil incarnate. your sister was light and love, and balanced you out. you have all the evil powers, you just have morals now. i think the choice system will be kept to staying alive. classes help you power up. and you gotta get revenge for your sister. also, there might be a love interest you actually care about.
yes, i know, more gameplay than story. im still working on it. i have a bunch more i could put down, but i think you guys have bleeding eyes already. yes, it would be a sandbox.
if you have any questions about the game, just quote this and ill tell you.