How to eliminate the wrong direction torque of stepper motor
The torque on the motor is a function of the current through the coils.  Back EMF created by the rotor moving causes a voltage.  Whether this voltage turns into a torque depends on what is connected to the coils.  If left largely on its own, like if the coils are shorted, the back EMF causes current that opposes the rotor motion.  For example, electronic braking of permanent magnet motors is often done exactly this way, by shorting the coils.  Your premise, and therefore your question, make no sense.