The father of Ken Nakajima and the owner of the ZAPPER motorbike shop in Sumida's Bokuto district, he is an old man who is an expert on motorcycles and was an excellent rider in his younger days. Now widowed, he is currently remarried to his second wife, Sena Wakabayashi. Though he is senile at certain times and his unthoughtful on certain matters, Daimaru still cares about Ken and Sena as they are his only remaining family left. He had a good impression on Miyuki when she kindly called him father, indicating that he still liked the younger generation to appreciate him like a caring parent.

He has a Ducati motorcycle that he uses personally. During his first encounter with Miyuki and Natsumi, Daimaru initially thought that Natsumi was Ken's girlfriend until realizing Miyuki was the better choice.

Due to his knowledge of motorbike handling, Daimaru tries to teach Ken techniques to befit his duties as a motorbike officer, to the point of "breaking him." He has a scar over his left eyebrow.

(Source: Wikipedia)