The Accursed, the Banished and the Regretfuls

Far long ago, the creator Veldanava thought of getting rid of his Omniscience and Omnipotence in order to exist as a part of creation and not something beyond it. Just before doing it, he looked one last time in the future of his creation, to be sure that nothing that could become a threat impossible to dealing with will spawn. But he overlooked something.

Countless years later, a odd demoness began to wreak havoc in the Underworld, an abnormal existence on par with the Primordials, who seek greater strength for a secret purpose.
Almost 2 century after her, a little blue blob appears in a sealed cave, ecstatic of being reborn in "this" world, who will allow him to save his life, even if he doesn't remember how or why. A slime, which possess only one half of a soul...

Authors note: This story will take place with a new Rimuru, former French (yeah, why not), but who has also grow up with some manga culture, different personality, and with ruling, combat and others skills from the start.
The demoness will be an OC linked to this Rimuru as family.

Small warning: Mature tag is for harsh thematics that will appear later in the story, like depression and its derivatives, or occasional depiction of violence, mostly mental. The tag isn't for lemons as they aren't put in this fic but will be gathered in the annex book alongside bonus chapters.
Still, dirty jokes will occur occasionally. This story will still have some relationships (mostly polyamorous) and fluffy moments.

Reminders: I do not own the rights to Tensura, or any other licences that will appear in a way or another.