Edens Zero: Who is the Demon King?

gamerant.com:

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.

Edens Zero: Shiki Granbell's Story has a Grave Ending

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