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 author can show Jason's jealousy through his actions. For instance, when Percy is praised for a successful mission, Jason might clench his fists or look away with a scowl. He could also be short - tempered with Percy in group discussions, interrupting him or making snide remarks.
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.
Jason could show care for Batman in fanfiction by having deep, heartfelt conversations with him, revealing a hidden soft side. He might also take on dangerous tasks alone to spare Batman from harm or work behind the scenes to gather crucial information that benefits Batman's endeavors.