This youngest of the triplets has a rare condition; Hyperumbrasis. Indeed, Cosmodeus's shadow has been bold and dark as ink since the day she was born. This also affected her mana. In the Mirandian System, most people are born with a blank Mana canvas, which they get to color in and expand with exposure and expression of magic, i.e. by casting spells and pursing knowledge in certain methods or elements. Contrary to this, Cosmodeus' Mana canvas has been steeped in Shadow long before she's even learned to cast her first spell. As a result, Shadow magic is the only type of magic she can use.

Cosmo has always been nervous and afraid of people, so she grew skilled at avoiding attention, even going so far as to develop techniques to erase her presence, such as a magic spell that makes her difficult to notice. It's a very effective spell, but there's one person it doesn't work on... Ryanne. Ryanne could see right through the spell with her keen eyes.

Ryanne has always looked at Cosmodeus and protected her. The two of them found they share a common interest in monsters, demons and abyssal creatures; Ryanne, who wants to become a Monster Queen, relies a lot on Cosmo's knowledge. And Cosmo, for her end, wants to visit the abyss someday, something she could only do with Ryannne's help. The two moved closer to the sea together for Ryanne's job as a Krakenbuster. They quickly came to confess their feelings to one another, so now they're in a highly functioning, open relationship ~ Ryanne gets so much of the attention in a crowd that Cosmo becomes invisible when she hides in Ryanne's shadow. In exchange, Ryanne gets Cosmo's support, from both her spells and her menagerie of Shadow familiars.

Cosmo's shadow menagerie is composed of 5 cute lil critters, all having their own abilities, even capable of fusing their form to Cosmo or Ryanne to improve their abilities. Cosmo's cat, her name Starlight, can chase off Shadow Pests and is an expert in stealth, improving her host's awareness and ability to hide in shadows. Her bunny, a little guy called Nuit, can remotely access Cosmo's secret grotto, and improve Cosmo's athletic abilities. Fontaine, a cheery and supportive bird, can survey the land and function as a second pair of eyes, relay messages, and her quills are an infinite source of ink for writing. She can also fuse with Cosmo, enabling her to fly with her wings. Blindness, the bat, can hear and locate things from far away, serving as a radar, and can use his high-pitched screeches for defense. He could also fuse with Cosmo to give her bat wings... but Ryanne called dibs.

And finally, there's Gouffre, the shadow gator. The most powerful and intelligent of Cosmo's familiar, he's an actual shadow demon capable of speech. His shadow is capable of biting with the grip strength of a bear trap. In actuality, he's mostly chill, and genuinely cares for Cosmo and Ryanne as friends. Whenever Cosmo has an anxiety attack, he's always there to reassure her when Ryanne can't. While he is a demon, his might is more physical and magical, so he can grant superhuman strength to whoever he fuses with.