Spoiler Alert: This content covers an arc from the Manga that has not yet appeared in the AnimeShiki inherited more than just the title of Demon King from his grandfather Ziggy. In the Year X492, Edens Zero's Cosmos is inhabited by both humans and androids, and an unlikely union is formed between The King of Robots and an abandoned human child.
Although not blood-related, the two become a family with a connection so strong that Shiki is able to "inherit" both Ziggy's title as the Demon King and his ability to use Satan Gravity. However, their relationship may not be as sturdy as first appearances suggest.
Ziggy - The King of Robots
When fans are first introduced to Ziggy, as the Demon King who raised a defenseless boy as his own, their hearts were instantly warmed. The android had previously been traveling across the Cosmos, with his Four Shining Stars by his side, in search of Mother, the Goddess of the Cosmos. Along his travels, Ziggy stumbles across an abandoned boy and puts a halt on his adventures to settle down on the planet Granbell to raise the child. The Demon King originated from Granbell himself, having been built along with multiple other robots for the Kingdom's amusement park. When visitors became scarce, the machines were left to fend for themselves, and so Ziggy built the Edens Zero and his Shining Stars and went in search of something greater.
Seemingly from old age, The Demon King dies years later at Shiki's side, after instructing Michael and the other androids to ensure that the boy finds the Edens Zero and broadens his horizons further than the small planet of machinery. His parting words to Shiki emphasize the importance of friendship and forming bonds with both people and machines. Unbeknownst to Anime fans, the Demon King is later revived in the Edens One Arc, and during the resurrection process, his system functions have been reset. Ziggy is reminded of his former self - fueled by his hatred for humans, with his sights set on the destruction of mankind.
Shiki Granbell - The King of Magimech
Following his grandfather's death, Shiki claimed the title of Demon King, reinforced by his discovery of the Edens Zero and his efforts to reunite the Four Shining Stars. Shiki is an exceptionally strong human, having learned all he knows about Ether from Ziggy and even inheriting his Satan Gravity Gear, which allows him to manipulate the forces of gravity. His parent's identities remain unknown, and Shiki seems completely unperturbed by this. Besides finding Mother, his main priority is to fulfill his grandfather's wishes by making 100 friends - but considering his lack of human contact over the years, his awkward interactions are thoroughly entertaining.
Officially his first new friends, Rebecca and Happy "rescue" Shiki from the planet Granbell following Ziggy's death, and the youngster quickly joins his new friend as a member of the Guild Shooting Starlight, making him an official Adventurer. It is not long before the trio discovers the Edens Zero and the first Shining Star, Witch Regret. The stunning android immediately acknowledges Shiki as the new Demon King and explains the connection between Ziggy, the Edens Zero, and the pursuit of Mother. But first, the Four Shining Stars need to be reunited, and the kind-hearted Shiki eagerly takes on the task. He is an honorable fighter who is willing to lay himself in harm's way to protect another - a defender of the weak and friend to all.
The Demon King's Ether Gear
This sci-fi anime focuses on the use of Ether Gear to power a select group of its characters- good and evil. Both Ziggy and Shiki possess the ability to use the Satan Gravity Ether Gear, famed for being the iconic weapon of the Demon King. This Gear gives its user the power to alter gravitational fields around a person or object, supplying them with a range of new strengths, including destructive energy balls. By changing the direction of the gravitational forces, Shiki gains the ability to levitate himself or others - almost like flying, but not quite. He can also create the opposite effect by applying the force downwards and essentially making the target heavier - a technique that helped Shiki destroy the indestructible Kurenai Dragoon, much to Madame Kurenai's surprise.
The fact that Shiki is capable of using Satan Gravity makes his claim to the title of Demon King indisputable. The Adventurer can also make himself the center of gravity, helping to propel his opponent towards him or even pull them out of the sky. He can increase his strength by absorbing kinetic energy and transforming it into gravitational energy to power up his attacks. When in Overdrive, the Demon King's true form is revealed, black horns and all, as Shiki's body transfigures to compensate for all the additional power.
Grandfather Ziggy
Although this is a sci-fi Anime with many lead android characters, not all robots are accepted as individuals, providing a major theme of tolerance to the story. There is a stark contrast between Shiki's unwavering acceptance of Ziggy as his grandfather and Homaru Kōgetsu's struggle to view Valkyrie with the same familial nature. The two humans were, however, raised in different worlds. Homaru was exposed to a mixture of humans and machines, whereas Shiki found companionship only in androids, having known nothing more until he found Rebecca and the Edens Zero. Both the Demon King and Valkyrie sacrificed everything when they found a child in need, forgoing all egocentric goals in place of satisfying the tiny human's needs. Such selfless acts demonstrate more "heart" than most humans are capable of - so why should possessing organs be a key component assessing the emotional capacity of an entity?