Note, this is the anime page for Akihiko, for the manga page: Akihiko Kaji.
The most distinguishing aspect of his appearance are his facial piercings including Akihiko's left lip, tongue, and two ear piercings with a gauge. His eyebrows are thin and short and he has eyes that are described as having a bad look to them. He has short blond hair on top of his oval-shaped face, the back of his hair is also short. Kaji has a muscular build whilst also being tall and has long legs.
He occasionally wears a baseball cap and often wears a black T-shirt. Akihiko tends to wear jeans held up by a belt and dark shoes.
Described as scary looking but a nice guy, Akihiko is exceptionally perceptive towards others noting right away that it was strange for Ritsuka to bring someone back, and later realizing why.
He likes working at a convenience store as he can take all the leftovers home. When beginning the band he did not consider the other members as the types who would bother getting to know each other at first, just interested in playing the music.
For the all covering story on Akihiko in the anime: Akihiko Kaji Anime/Story