Turbo. This is what it does.
Press T (default). It shows an aura around you. It increases your KI by a certain ammount, but it drains it while using it. It's just a power boost.
Press T Again, and it will turn off. To configure Turbo, hit ESC, goto options, keyboard, look for the AURA, and bind it to whatever button.
Quick summary:
Press once: turns on aura, giving you a slight boost making you faster.
Press again: turns off aural, bringing your KI back to original state.