 Ryu can defeat enemies by attacking with his Dragon Sword or by using secondary weapons which consume Ryu 's " ninja power " ; such weapons include the following : " Windmill Throwing Stars " which move back and forth like boomerangs , " Fire Dragon Balls " which launch fireballs downward at an angle , the " Fire Wheel Art " which launches fireballs upward at an angle , the " Invincible Fire Wheel " that forms a series of rotating of fireballs around Ryu and destroys any enemy who comes into contact , and a new weapon in this series called the " Vacuum Wave Art " which hurls vacuum blades above and below Ryu simultaneously . Players can collect red and blue capsules to refill Ryu 's ninja power , and they can also collect " Scrolls of the spirit of the Dragon " to increase Ryu 's maximum ninja power level . Another new item in Ninja Gaiden III is the " Dragon Spirit Sword " that increases Ryu range of his sword . At the end of each Act is a boss which has its own life meter that decreases when damaged ; Ryu can defeat the boss by completely depleting its life meter . Ninja Gaiden III 's first four bosses consist of the " bio @-@ noids " – super @-@ human creatures created and controlled by Foster to take over the world ; they each represent the four elementals : earth , wind , fire , and water . 
