This enables the Passive Mode feature from the Options menu, which is used to disable PvP on all but Kill Zone floors (does not work on Floor 6 or Floor 13). Only PvP from accepted Duels or when in Kill Zones floors are allowed (meaning you cannot damage other players, and they cannot damage you). It can only be toggled on / off from Safe Zones such as Floor One, Towns, and most Teleport Pads.