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.
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.
Yes, there are some out there. However, 'lemon' in fanfiction often implies adult - themed content which might not be suitable for all audiences. You can try searching on some fanfiction platforms like Archive of Our Own, but be aware of the content ratings and warnings.
Iori Yagami was a famous swordsman in the martial arts novel," The Eight Dragons ". His story told that he had traveled to a different world, where he learned different martial arts and became a top swordsman. He had experienced many challenges and adventures in his life and made many friends. He was willing to sacrifice himself to protect his country.
In the manga, Sukuna doesn't possess all 20 fingers. There are specific story arcs and events where his finger count changes based on the plot developments.