Warning! Spoilers ahead for Ghost Reaper Girl chapter 30!
It's no secret that mangaka Akihisa Ikeda aka Akissa Saiké found a great deal of inspiration from H.P. Lovecraft's Ghost Reaper Girl. There are characters he named after certain Cthulhu gods or monsters but who don't share many or any other similarities with their namesakes beyond what he decided to call them. There are also characters he took straight out of the pages of Lovecraft's fiction like Cthulhu, the Great Old One himself.
Then there are instances when Saiké expands upon Lovecraft's preexisting mythos to create something wholly new but still unmistakably Lovecraftian. An example of this is Saiké's version of Yog-Sothoth, Lovecraft's cosmic entity and Outer God that embodies all of time and space across an infinite number of space-time continuums. Yog-Sothoth is known for lurking outside of the known universe, serving as both the gate and key to the vastness of the Multiverse. In Ghost Reaper Girl, Yog-Sothoth gives the spirit Kai Iod "the silver key" so he can open the gates of Hades himself, even though Lovecraft's Yog-Sothoth is the actual key and the key actually leads to the true vastness of what is. Because he could unleash the horrors of Hades with Yog-Sothoth's key, Kai Iod was once known as the Yog of Destruction, which is a term proprietary to Ghost Reaper Girl as the only Yog is Yog-Sothoth himself.
The fact that Kai Iod can bring about destruction by using Yog-Sothoth's key almost matches with H.P. Lovecraft's original mythos. Like most of Lovecraft's Great Old Ones and Outer Gods, a great many cults follow Yog-Sothoth, and those who foolishly seek his favor are beset with calamity and ruin. But rather than Kai Iod experiencing those things, he is the one who brings that calamity and ruin to the people he chooses.
Kai Iod also once served another Lovecraftian god-like entity known as Oscar Cthulhu who never appeared in Lovecraft's fiction but who is obviously related in some way to Cthulhu, which, Ghost Reaper Girl, is the name of a species, not a specific character. Not much is known about Oscar like, for example, if he is the Great Old One's sibling or offspring, which wouldn't deviate too much from the original mythos since Lovecraft's Cthulhu actually has a vast family tree, though, none of them take on a humanoid shape like Oscar. What readers do know is that Oscar obviously has a power over Kai Iod that coaxes out his inner darkness. Kai originally believes that he killed Oscar, allowing him to serve his new master Chloe Love. But once Kai learns that Oscar is still alive, he has no choice but to revert back to his old ways and become the Yog of Destruction.
Although Ghost Reaper Girl has been on hiatus since November 1 due to Akissa Saiké's poor health, the manga will finally resume on December 28 with chapter 31, which will see Chloe Love as she attempts to restore Kai to how he was before Oscar Cthulhu reverted him back into the Yog of Destruction, allowing the spirit to open up the gates of Hades.
