In the original series, he looked very similar to Kiyama Hiroto, but his hair color, eye color and skin tone were darker. Coincidentally, his casual clothes were exactly the same as Kiyama Hiroto's, but his jacket was blue in color instead of pale green.
In the timeline of Ares no Tenbin, he has a fair skin tone and a messy, short, seaweed-like gray hair with some bangs tinted white. He has pale red eyes and a blue lightning-shaped tattoo that covers from his left cheek up to his left eyebrow. His casual clothes consists of a striped black shirt, as well as pants and shoes of the same color. He also wore a silver ring on his right hand, several bracelets on his right wrist, one in the left and a silver pendant around his neck.
Not much is known about Kira since he only appeared in flashbacks, but he loved soccer and wished to be a professional soccer player. However, while studying soccer abroad, Kira was killed mysteriously and the actual cause of his death was never revealed. The case was then closed as an accidental death due to a government official's son being somehow involved. This caused his father, Kira Seijirou, great grief and sadness which made him want to revenge over the soccer world. Kiyama Hiroto was also named after Kira.