Keith just before hitting Bio-Magnetism.
Bio-Magnetism is the completed version of Gemini. In its early stages, Bio-Magnetism was developed by Keith in The Prince of Tennis: Eikoku-shiki Teikyū-jō Kessen! out of anger when Xiu was injured by the opposing doubles team. Even in its early stages, Keith was able to leave an opponent deaf and blind.
Keith accumulates a large amount of air in his ball before he hits it and the air is released from the ball as it speeds towards the opponent. The force of the air is powerful enough to knock his opponents off their feet. The technique is incredibly dangerous, capable of knocking his opponent off their feet and flinging them backwards or into the air. Furthermore, the ball has so much force that it can break through the structures of the ground, wall, and ceiling. It is a technique that focuses on injuring the opponent and preventing him from ever playing tennis again. This can be used as both a serve and a return.
Although Keith can hit Gemini with his left hand, he only hits Bio-Magnetism with his right hand. Keith seals this technique by playing with his left hand.
Variations[]
When playing inside of Atobe's castle, Keith aims the shot at the ceiling, causing the force of the ball to crush Ryoma into the ground. The aftershocks of this variation of Bio-Magnetism are also able to toss Ryoma around in the air while he is unable to do anything.
Ryoma is also capable of hitting a variation of Bio-Magnetism where air is collected at the back of the ball, rather than the front, to accelerate it.
Countering Bio-Magnetism[]
Ryoma avoids being slapped around by the technique by dropping to the ground as the shot approaches him, then enters the air sphere and allows it to carry him. Ryoma is able to return the shot in mid-air. This counter works because Ryoma is able to penetrate the exterior of the Bio-Magnetism sphere that would otherwise hit him with the force of a wall. Once inside the sphere, it becomes significantly less dangerous.
After Keith begins to aim the shot at the ceiling, Ryoma is able to counter it by hitting his own Bio-Magnetism in return. It should be noted that Ryoma switches to his left hand before he begins to use Bio-Magnetism himself.
It is possible to return Bio-Magnetism without the use of another Bio-Magnetism, but it expends a lot of energy and strains the receiver's wrist.