This is Author's note as there are a few things i feel the need to explain so i don't have to do it for the actual first chapter. also i do not own the cover for this nor do i know who made this amazing picture but who ever it is the credit goes to them for this awesome picture, also if i had anyway to do it Cc would be first in the harem.

First is scenario, Magical beings exist and are known to humans minus Devils, Fallen Angels and Angels, so Britannia treats them just as bad as Numbers, and also Britannia nuked all the places they conquered to drive the "Numbers" and nonhumans underground (sort of like Metro with the nuclear apocalypse) so there will be underground cities that started in the metro's till they eventually were able to make pathways and find underground rivers and lakes, and yes there would be purifiers that allows the water to be drinkable, magic helps keep the underground stable and helps grow food, the last and worst nuclear attack was in Japan, forcing Godzilla to awaken, yes Godzilla's in this but his history is explained later in the story and not right away due to his retaliation against Britannia all the Nuclear warheads were destroyed and never created again due to fear of facing Godzilla's wrath, he's the only being in existence even Britannia fears, on to further things Yggdrasil was created by the Chinese and like in the anime of Overlord was around for 12 years, and for 6 years was played by Lelouch till the final days.

Second are a few characters

Lelouch Ainsworth (Lelouch Vi Britannia) an exiled prince who lived in Japan for a few months lived at the Kururugi Shrine, after the war ended he and Nunnally were separated from Suzaku and later adopted by Elias Ainsworth and is a current resident of New Osaka, Guild Master and Ruler of the Guild Ainz Ooal Gown.

Nunnally Ainsworth (Nunnally Vi Britannia) an exiled princess and younger sister to Lelouch, blinded due to witnessing the death of her mother and crippled by the terrorist attack that took her mother's life, soon cured of her blindness by her foster father Elias and eventually healed her legs, she is a current resident of New Osaka.

Akari Ainsworth, an NPC created by Lelouch to play the role of sister in Yggdrasil, has crimson red hair and her eyes are pure blue and can glow, her race is Dragon God

Elias Ainsworth, a mysterious magus that is neither human or fey, many centuries old, he journeyed to Japan at the request of a friend to find Lelouch and Nunnally and due to the nuclear attack he decided it was safer for them to remain with him in Japan as they traveled to to Osaka where the survivors eventually created the underground city New Osaka which he is a resident and helps serve as a doctor and supernatural expert to the city, and is a council member.

Alisha Diphda, an exile nobles daughter who decided to follow Lelouch and Nunnally to Japan, she remained loyal to Lelouch as she became his Knight of Honor before the death of Lelouch's mother, she is also tasked with defense of her new home of New Osaka.

Kaori Kanzaki, a young Japaneses woman who was favored pupil to Kyoshiro Tohdoh, distrusting of the Lelouch and Nunnally at first but eventually becoming friends with them she followed them to their new life in New Osaka at her teacher's request.

Master Splinter, a wise old Wererat and old friend of Elias, master of many of the Japanese styles of fighting, he like Elias is a council member of New Osaka and serves as Elder to the city.

Yue, a young Wererat who is the daughter to Splinter and the same age as Lelouch, she trained under father to be a protector, she is also childhood friend to Lelouch and Nunnally when New Osaka was being made, she and Lelouch have been in a relationship for a few years.

Just to make this clear TMNT is not in the story just Splinter, Yue is a female version of Splinter from a fanart I found on DA that belongs to Chochi, check out his artwork, and also interspecies relationships are a thing here so please no hate and leave positive reviews or if you have any questions please leave me a note.

Alisha Diphda is from Tales of Zesteria, Kaori Kanzaki is from Index and Elias is from Ancient Magus Bride.