One year ago, a UFO containing 150 aliens crash-landed off the shores of Kasai. Because no one could fix their ship, the Japanese Government decided to bestow upon them the designation DearS and make them into Japanese citizens, teaching them the language, customs, and culture of Japan. However, in order for them to become more familiar with human society, a home-stay program has been enacted to allow them to mingle with other humans. One misty morning, a truck carrying a capsule that housed one of these aliens ends up dropping it into the riverbank, releasing her from her confinement. She is eventually found by a high school student named Takeya Ikuhara, who saves her from being hit by a truck and takes pity on her, despite being extremely distrustful of their race and wanting nothing to do with them. Upon being named Ren, she imprints upon him as her Master and serves as his personal Slave, leaving him with a DearS who wants to remain with him no matter what and bringing his ordinary, alien-free days to an end.

Brutal murders, petty thefts, and senseless violence pollute the human world. In contrast, the realm of death gods is a humdrum, unchanging gambling den. The ingenious 17-year-old Japanese student Light Yagami and sadistic god of death Ryuk share one belief: their worlds are rotten. For his own amusement, Ryuk drops his Death Note into the human world. Light stumbles upon it, deeming the first of its rules ridiculous: the human whose name is written in this note shall die. However, the temptation is too great, and Light experiments by writing a felon's name, which disturbingly enacts his first murder. Aware of the terrifying godlike power that has fallen into his hands, Light—under the alias Kira—follows his wicked sense of justice with the ultimate goal of cleansing the world of all evil-doers. The meticulous mastermind detective L is already on his trail, but as Light's brilliance rivals L's, the grand chase for Kira turns into an intense battle of wits that can only end when one of them is dead.

After death, either Heaven or Hell awaits most humans. But for a select few, death brings them to Quindecim—a bar where only pairs of people who die at the same time can enter. Attending the bar is an enigmatic figure known as Decim, who also acts as the arbiter. He passes judgment on those who wind up at Quindecim by challenging them to a life-threatening game. These games determine if the patron's soul will reincarnate into a new life, or be sent into the void, never to be seen again. From darts and bowling to fighting games, the true nature of each patron slowly comes to light as they wager their souls. Though his methods remain unchanged, the sudden appearance of a black-haired amnesiac causes Decim to reevaluate his own rulings.

It was just a usual morning. Akira Shiroyanagi, a high schooler who loves games and Konpeito (Japanese sweets), has suddenly been dragged into a battlefield by a mysterious girl who calls herself Mion. The participants are told that they are erased from the family register, involved in an experiment, and gained certain powers. Akira is determined to win the game with his newfound powers and destroy the organization. Armed with a power no one expects and his brain skills, the new period of intelligence battle begins! (Source: MU, edited)