so use a keyboard with a usb plug in. start up the game. go to a hideout and go to the bed. sit in it. while in your powers menu highlight a power and press A. while the screen is transitioning press and hold the keys letter O and Letter P at the same time. and your xp will go up.
It took roughly 120,000 xp for me to level everything up from Lv 1.
This is a huge exploit and kinda ruins the game. cause it is so tempting to do this to get the good ending of the game.
here is a how to video.