Alayoho

Deus is an ancient deity who has ruled over time and space and the laws of causality. As god, Deus is very powerful and is able to create and alter causalities through time and space. It is implied that he may be able to rewind time, but leaping back in time can create parallel worlds. Despite being a god, Deus is unable to resurrect the dead. While reviving a body is possible, without a soul, the dead cannot come back to life by any means. Deus has control of the Akashic Records, the universal compendium of knowledge and history. Deus is shown to be able to create artificial lifeforms, namely Aru Akise, revealed to be his "Observer" in the survival game to keep track of the ever changing futures of the diary owners.

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Deus in the Cathedral of Causality.

Deus operates from the Cathedral of Causality, depicted as a large domed building coloured with a purple tint. Deus sits in a large throne which hovers above the ground. The cathedral also has an arena where the diary owners, Deus and Muru Muru meet for occasional meetings. The arena is covered with an eternal cloudy sky, revealed to actually be a cover for the Akashic Records.

He remains oblivious to the existence of the first alternate world, implying he only has power over the time and space of the universe he lives in. Deus at first makes the choice to not interfere with the events of the game and watches merely as an observer. However, during the second game, when Yukiteru Amano discovers the three corpses in Yuno Gasai's house, the whole pre-planned events of the second survival game are altered, and Deus does not act to restore it, finding the alternate path all the more interesting. He eventually abandons his intention to not influence the events of the game after Muru Muru does. He wishes to make the game as fair as possible, but outside influences force Deus to play his hand near the end of the game to ensure it runs smoothly. He is even willing to abandon the game all together, as seen in the third world when John Bacchus puts a halt to his Future Diary project, cancelling out the third survival game.

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Deus and John Bacchus formulated the Survival Game

Deus appears to have extended relationships with the different diary owners. He is rather fond of Yukiteru, at first posing as his imaginary friend and personally makes him the "First" diary owner. Deus openly supports Yukiteru throughout the game, unphased by Yukiteru's mishaps and believes it is all part of Yuki's future to win the game. He also has a unique relationship with Minene Uryu, who does not believe in god and wants nothing more than to rid the world of the very concept of a deity. Minene has a love/hate relationship with Deus, openly hating him but is willing to ask him for advice, and even protests to receiving a portion of his powers when the time comes. Deus views Minene as an ally, using her to put a stop to Muru Muru's plans. Deus and John Bacchus seem to be good friends, creating the Future Diaries together. John seems to care for Deus, but also uses Deus' needs as an excuse to extend his own plans in the survival game, requesting that Yukiteru and Yuno be eliminated from the game to speed it up before Deus dies.

It is never explained why Deus is dying, but his death causes the universe to be swallowed up in black holes. Deus is succeeded three times in the series. In the first world, Yuno becomes his successor, Yuki in the second, and finally Yuki and the third Yuno from the third world