While trying to rescue a cat, martial artist Ryo Sakazaki and his playboy best friend Robert Garcia unwittingly break into a jewel thief's apartment. Moments after entering, they witness the thief being murdered by a group of thugs. Despite fighting their way out and escaping, things go from bad to worse when Ryo and Robert learn that the thugs were working for Mr. Big, the biggest crime boss in South Town. Not only does Mr. Big believe that the two have stolen the "Eye of Sirius," a priceless diamond, but he has also kidnapped Ryo's younger sister Yuri, and is holding her hostage. Without the diamond and out of options, Ryo and Robert must fight their way past Mr. Big's men and save Yuri before it's too late.

The story takes place on a world 100 years in the future, a few years before Lisa and Lorna joined eX-D organization. The world where people drives computer-controlled electrically powered "AI cars" which automatically take you where you want to go. However, one AI car mysteriously start to run amok. Now Nina and Rei, as the main driver for ex-D organization have to solve the mystery behind the AI car with evil plot and trap awaiting for them...

Transfer student Takisawa Noboru quickly learns that all disputes at his new school are settled in the boxing ring. Now he finds himself in a series of showdowns with the local top dog, Ibuki Saburo, for the love and respect of the beautiful Yukari.

The story revolves around a girl named Yuuka, who encounters a being from the depths of the Earth named Chii-chan (a pun of chiteijin, the Japanese word for underground-dweller), and an alien named Ucchan (a pun of uchuujin or alien). The story follows their heartwarming and chaotic everyday lives together.