One common theme is isolation. The unwanted child often feels alone in the wizarding world, just like Snape did in his own way. They might be shunned by others because of their connection to Snape or their own unique situation.
One popular Severus Snape unwanted child fanfiction is 'The Unwanted Heir'. It delves into the life of a child who is related to Snape but feels unwanted in the wizarding world. The story is filled with complex relationships and the struggle of the child to find their place.
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.
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.