Once Kunoichi and Ninja have reappeared on the screen, you'll have to begin walking to the right, as three light-green-uniformed soldiers come running towards you from the right side of the screen; once you have stabbed (or thrown a shuriken at) each of them to kill them, two light-blue-suited, demonic-masked, twin-sword-wielding male ninjas will materialise in front of you (and unlike the three you faced on the third stage, these ones can dematerialise when they are about to be stabbed, then rematerialise elsewhere on the screen, so you have to kill them quickly to finish the stage within the time limit).
Once you've stabbed both of these ninjas four times (or thrown four shurikens which do not get blocked at them) to kill them (their deaths are also worth ten additional shurikens), eight more light-green-uniformed soldiers shall come running towards you from both sides of the screen; once you've killed all of them, a purple-suited gangster shall emerge from behind a building, and fire an infinite amount of shots at you. Once you've thrown a shuriken at him (while not getting too close to him) to kill him, fourteen more light-green-uniformed soldiers will come running towards you from both sides of the screen - and once you've killed all of them, another purple-suited gangster will emerge from behind another building and fire an infinite amount of shots at you. Once you have thrown a shuriken at him from a distance to kill him, a dark-green-uniformed soldier and five teal-uniformed soldiers shall come running towards you from the right side of the screen (alongside a non-attacking dark-green-uniformed commander); if you don't kill all seven of these enemies quickly enough, the commander shall order Retreat! from the Yamaha YM-2610, and any survivors (including the commander himself) will run back off the right side of the screen. Four more light-green-uniformed soldiers shall now come running towards you from both sides of the screen while another dark-green-uniformed soldier drops down to the ground in front of you and fires four shots at you - and once you've killed all of them, three attack dogs shall come running towards you from the right side of the screen. Once you crouch down and kill all of them, a third dark-green-uniformed soldier shall drop down to the ground in front of you and fire four shots at you; once you have killed him, two more light-green-uniformed soldiers will come running towards you from the right side of the screen while two more attack dogs come running towards you from its left side. Once you have killed all of them seven more attack dogs will come running towards you from both sides of the screen - and after you've killed all of them two ochre-uniformed soldiers shall come running towards you from the right side of the screen and fire a shot at you. Once you've killed both of them, a third purple-suited gangster will emerge from behind a third building and fire an infinite amount of shots at you; once you have thrown a shuriken at him from a distance to kill him, twelve more attack dogs shall come running towards you from both sides of the screen. Once you've killed all of them, a fourth purple-suited gangster shall emerge from behind a wall and fire an infinite amount of shots at you - and once you've thrown a shuriken at him from a distance to kill him, four more light-green-uniformed soldiers and an identical amount of additional attack dogs shall come running towards you, from both sides of the screen. Once you've killed all of them, a fourth dark-green-uniformed soldier will appear in front of you; once you have killed him, a fifth dark-green-uniformed soldier and five more teal-uniformed soldiers will come running towards you from the right side of the screen alongside another dark-green-uniformed commander. Again, if you don't kill all seven of these enemies quickly enough, the commander will order Retreat! from the Yamaha YM-2610 and any survivors (including that commander himself) shall run back off the right side of the screen - and a fifth purple-suited gangster shall then emerge from behind another wall to the rear of you, and fire an infinite amount of shots at your back (he shall also not emerge until both players have passed him).
Once you have turned back to the left and thrown a shuriken at this gangster from a distance to kill him, a thirty-sixth light-green-uniformed soldier will come running towards you from the left side of the screen; once you have killed him a tank shall start to be heard from the Yamaha YM-2610, so once you have turned back to the right, you shall occasionally have to stop walking in that direction, as the shells this tank is firing at you explode in front of you. Once the tank rolls into view from the right side of the screen, its driver will also start firing shots at you from the machine gun that is mounted on top of its turret - and once you've jumped up and thrown two shurikens at the driver, he shall duck back down into the tank's turret, so you will have to jump onto the tank's body, and drop back down off the other side of it as its turret rotates 180 degrees. The tank shall then reverse back towards you, while its driver re-emerges from its turret (and continues firing shots at you from its machine gun); once you've turned back to the left, jumped up and thrown two more shurikens at the driver, he'll duck back down into the turret again and you will have to jump back to the left onto the tank's body, turn back to the right as six winged mutants come flying towards you, kill all the mutants (their deaths are also worth thirty more additional shurikens), turn back to the left again and drop back down off the other side of the tank's body once more (as its turret is rotating 180 degrees for a second time). The tank's driver shall then re-emerge from its turret again, and continue firing shots at you from its machine gun - and once you jump up and throw a fifth shuriken at him to kill him, the tank shall momentarily stop moving while the driver's corpse falls out of its turret onto its body and off the bottom of the screen but it shall then reverse its direction towards you again, so you must jump back to the right onto its body and drop down off the other side of it once again (after it has gone, the sound of its engine shall also stop, but there is still a second tank that you will have to face at the end of the stage).
Three more light-green-uniformed soldiers will then come running towards you from the right side of the screen; once you've killed all of them, a fortieth light-green-uniformed soldier shall appear in front of you. Once you've killed this soldier, a sixth dark-green-uniformed one and five more teal-uniformed ones shall come running towards you from the right side of the screen (alongside a third dark-green-uniformed commander) - and for a third time, if you do not kill all seven of these enemies quickly enough, the commander shall order Retreat! from the Yamaha YM-2610, and any survivors (including that commander himself) shall run back off the screen's right side. Three more light-green-uniformed soldiers will then come running towards you, from both sides of the screen; once you have killed all of these, a sixth purple-suited gangster will emerge from behind a fourth building to the rear of you and fire an infinite amount of shots at your back (again, he will also not emerge until both players have passed him). Once you turn back to the left and throw a shuriken at him from a distance to kill him, two more ochre-uniformed soldiers shall come running towards you from both sides of the screen and fire a shot at you - and once you have killed both of these, three more light-green-uniformed soldiers shall come running towards you, from both sides of the screen. Once you have killed all of them two more dark-green-uniformed soldiers will come running towards you from both sides of the screen and fire four shots at you; once you have killed both of them three more light-green-uniformed soldiers will come running towards you from the right side of the screen. Once you kill them all, two more ochre-uniformed soldiers will come running towards you from both sides of the screen and fire a shot at you - and once you've killed both of them four more light-green-uniformed soldiers shall come running towards you from both sides of the screen. Once you have killed all of them, another tank will start to be heard from the Yamaha YM-2610 so you will again occasionally have to stop walking to the right as the shells this second tank is firing at you explode in front of you; once the tank rolls into view from the right side of the screen, you will have to repeat what you did for that first one earlier in this stage. Once you've killed the tank's driver and the tank has reversed its direction towards you for a second time, you'll have to jump back to the right onto its body, then drop down off the other side of it for a third time - and once you've done so, Kunoichi and Ninja will jump down an open manhole on the right side of the screen. Both players will now receive a bonus of 50 points for every shuriken they have remaining (followed by one of 30 points for every fragment of energy they have remaining), and proceed to the fifth stage (which is based in a sewer).