Kai is a normal sized individual with very little muscle mass to him, What he lacks in Physical appearance he makes up for in style. Normally Kai goes around in a Suit and tie, Wearing his formal clothes everywhere, Even into battle. With his black hair and Violet Purple eye's a single gaze from him has a certain Transfixing quality.
Kai was born the Son of Cobra and Kinana, His mother being a member of Fairy tail he was naturally raised around the guild and even tutored by some of the older Dragon Slayers (Gajeel specifically) when it was discovered he had a natural dragon slayer ability, This ability was then dubbed 4th Generation Dragon Slayer magic, Magic granted to the user because of his or her parents use of the magic. Because Cobra had a Dragon Slayer lacrima in his body so long it began to fuse with his DNA, And since Sound magic was his magic before he was infused with the Lacrima it was Sound Magic.
Kai was trained from an early age how to use his Dragon Slayer magic, His best friend the female mage Mysty Gryder was there to see him on his way to becoming a powerful mage, Often encouraging his friend to pursue the same goals he and Mysty quickly grew through the ranks of Fairy Tail, Confident enough to try to gain S Class status, However, After being beaten by Holy Fist Clive even with the help of Another mage they were turned down.
Dragon Slayer Magic is a type of Lost Magic which allows its users to transform their physical bodies into a Dragon. As a result, the user can transform their body with features of their respective element, utilizing both offensive and defensive styles. A Dragon Slayer is immune to the effects of their own element, and can consume external sources of their element to replenish their strength. However, a Dragon Slayer cannot consume the element that they produce themselves, and elements must be consumed through the mouth. It is known that certain Dragon Slayers have been able to consume elements other than their own, allowing them to combine both elements into one inside their bodies and use them to increase their abilities. Dragon Slayer Magic is the only way to kill, or even hurt Dragons, who are shown to be mostly unaffected by other forms of Magic.
Kai is a Fourth Generation Dragon Slayer and One of the first of his kind, Since it was a magic passed down to him VIA Genetics. Kai's Dragon Slayer magic utilizes Sound rather than a Physical Element, Because of this when he hears sound his body gains more and more power, Verbal Spells are practically nullified against him since he can just consume the power of the Sound Waves.
With Sound Dragon Slayer magic Kai can encase his body with sound waves and form a thick defensive shell around his body, Super exerting a pressure to keep most energies away from his Physical Form, However, If push comes to shove he can use the sound Offensively, By claws growing from his hands he can inject the claws into his opponent and fill them with sound waves.
Kai's Sound Dragon Slayer magic has many applications, His favorite is leaving people transfixed in a Trance like state or confusing them, Even causing severe pain by making sounds that can barely be heard by the human ear, Sounds almost Lethal to other Dragon Slayers. Anything that Sound can do, Kai can use it to his advantage, Even his roar is more powerful since The sound waves coming from his body have more of an impact.