This teensy missile has enough fuel to be able to turn around (assuming it is carried pointing forwards?) and then intercept an incoming missile? There doesn't seem to be enough room for the motor, the fuel needed to accelerate, control surfaces to make a tight turn, and a warhead big enough to make a difference?
The best defence against something coming from behind would be a raipidly-deployed metallic balloon, like an airbag that gets left in the space between the missile seeker head and the aircraft, while it makes a hasty retreat.