For nearly the entire Ninja episode, Dave is in his traditional Ninja garb similar to Elise's.
At the end of the episode, and every appearance after that, Dave sports a red t-shirt with his shop's name, blue jeans, and green and white trainers. Topped with a little paper hat pictured with a cookie.
His hair seems typical of Japanese youth (specifically the "deliquent-type"), with the sides and back kept short or shaved off and long with a wild frontal style.
Dave first appeared in "The Ninja", where he attempted to assassinate Elise for becoming a rouge. He surrendered after losing a fight with Elise. He then revealed to them that his entire ninja clan was wiped out in a bus accident.
Dave redeems himself and opens a cookie shop called "Ninja Dave's" in the city and offers Dan, Chris, and Elise free cookies.