For any of them: Various ancient mythologies are dragged kicking and screaming into the modern age, where they are made into a card game that is sometimes played by people who are dead or possessed by monsters from another dimension. The fate of the world frequently depends on the result.
Yumeiro Patissiere!: A girl likes to cook sweets and goes to a school with candy fairies and three boys that are really good at cooking.
Zatch Bell!: A emo genius gets a shotaro prince boy from another world that can spit lightning from his mouth as gift from his dad for his fourteenth birthday.
Or: Lazy genius high school student receives a six year old for his birthday and goes on a book-burning spree.
Or: A high school student, a pop idol, and a movie star exploit small children to fight their battles.
Zegapain: High school student meets a mysterious beauty who wants him to play a mecha video game. Except the game is real and the real world is the video game.
Zero In: High School students work part-time as Super-badass Rent-A-Cops.