Naoki Kuzumi, a junior in high school, had lost his parents in an accident five years ago, and is living with his aunt, uncle, and cousin Matsuri. He always thought his life was ordinary, besides the fact that he can't remember what happened in his youth. One sunny day as he is taking a nap on a bench, a redheaded girl -- Mikoto -- literally falls on him from the sky. For some reason, she thinks he's her younger brother. Naoki's time period is a temporal shelter for those in the future, when many are suffering from an incurable disease. When she heard her younger brother Yuusuke had been taken to Naoki's time, Mikoto herself had gone back in time.

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.

Set in an alternate version of the Meiji Era, a boy named Sakamoto Ryunosuke returns to Kyoto from Shanghai with his monster (youkai) Nekomaru. The law states that in order to live freely with humans, a youkai must be liscensed. The Kidou Shinsengumi Co. Ltd. is responsible for the capture of unliscensed youkais but must fight with the Tsubamegumi, who resents the new law. It turns out that Ryunosuke is the son of the owner of the Shinsengumis.

AD. 2023, Tokyo. Because of the change of the society such as internationalization and enlargement of the trading, the dark side of the society also continues changing. The criminals are getting deep, and their organizations are increasing its size, then the peace and security is getting worse. The government takes it seriously, and decides to introduce an innovative system. In order to cope with the special criminals, an extralegal police is founded. It is a special criminal team, Warriors, which consists of a few elite members. (Source: AnimeNfo)