No. Ryomen Sukuna is a fictional character from Japanese mythology and modern manga/anime. He doesn't have a basis in a true historical event or person.
Nope. Ryomen Sukuna has no basis in reality. It's a product of the creative minds of the writers and illustrators who designed a captivating fictional character for the enjoyment of the audience.
It could be other elements from Japanese folklore. There are many supernatural beings and concepts in Japanese mythology that might have influenced his creation.
Sukuna does die in the manga. The way it happens is quite dramatic and ties in with many other elements of the story, adding depth and tension to the overall narrative.
The Harry Potter fandom is great for oc fanfiction. There are so many aspects of the wizarding world to explore, like creating a new student at Hogwarts with unique magical abilities. Another good one is the Star Wars fandom. You can create original characters within the vast galaxy, perhaps a new Jedi or a smuggler in a far - off system. The Marvel Cinematic Universe is also a top choice. You could develop an original superhero or villain with powers related to the existing lore.
One of the top fandoms for fanfiction is the Doctor Who fandom. With its time - traveling and space - exploring premise, the possibilities are endless. You can create new adventures for the Doctor and his companions, or introduce new alien species. The Supernatural fandom is also very popular. There are so many different mythologies and creatures in the show that you can base your fanfiction on. And then there's the Percy Jackson fandom. It combines Greek mythology with modern - day settings. You can write about new quests for demigods, or explore the relationships between different characters from different cabins at Camp Half - Blood.