This page is dedicated to non-canon speculation, and information on it should not be treated as fact. Many of these theories/ideas, however, are very likely to be true.
Please feel free to add anything not already mentioned.
Artamos' Human/Pre-Cursed Form Edit
Before Artamos was a robotic rabbit head, he was said to be a large rabbit and a ladykiller.
Recently, Mogeko posted an artwork on their website of a character with rabbit ears and various other features suggesting they were somehow related to Princess Tosatsu, including similarly slanted eyes, nails, and outfit. As well as this, Mogeko's character Satanick posed behind this character with a sign; on it, the sign had a picture very similar to Artamos' rabbit form (seen as a silhouette in-game). The character is also surrounded by Tosatsu Soldiers.
He was said to be cursed by a witch, and it can be easily assumed the witch to do so was Tetsuzora, as she has a theme having to do with gears and mechanical parts.
It is extremely likely this is truly Artamos' human form, but Mogeko has yet to comment on it.
This theory has been confirmed true through some of the new comics on his website.
Artamos and the Sea God are Related/Close Edit
If it is assumed that Artamos' human form is truly the one seen in the artwork above, it can be noticed their attire is strikingly similar to that of the Sea God, down to the markings under the eyes.
Mogeko has not said anything concerning the similarity of their appearances, and it is possible it is simply coincidence.
Irena's Sister Edit
Irena has a sister that is visiting land, but their name is never mentioned.
It is possible this sister is Reley-Lo, as she is the only other known mermaid character of Mogeko's design (that is not Miyura). She appears to have a similar eye color to Irena, and dresses in a sailor-like fashion.
Vendetto is Ivlis' Son/Poemi's Brother Edit
Many facts suggest Vendetto is Ivlis' son, Ivlis being the main antagonist of The Gray Garden.
Vendetto is said to be good friends with Emalf, a demon that works under Ivlis, and they often do karaoke together. Poemi, Ivlis' daughter, is said to have a brother, but this may be referring to the other canon son of Ivlis' ,Licorice. Vendetto mentioned his father is an "airhead" in a bonus room scene, and that word can describe Ivlis.
When questioned, Mogeko chose not to speak about it.
It's been confirmed that either Satanick or Ivlis is his father on a recent drawing form their site.
Wadanohara's Mother is the Moon Edit
While Wadanohara was born from an egg, it is unknown who her mother was, or if she even had a mother.
The moon is heavily associated with Wadanohara/Meikai and is a recurring theme in the game, and it can be suggested it had something to do with her existence.