I'm not sure specifically as I haven't read it. But generally, a graphic novel combines visual art with storytelling. 'Sonne und Beton' might be about various themes like urban life (since 'beton' means concrete in German, could imply an urban setting) and perhaps something related to the sun which could symbolize hope, warmth or new beginnings in the context of the story.
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.
Since I'm not familiar with this graphic novel, it's difficult to determine the main characters. However, given the title, there might be characters who are either trying to escape from a cold, concrete - like existence (represented by 'beton') and are drawn to something symbolized by the sun, like hope or a better life. Or perhaps there are characters who are part of a world where the sun and the concrete play important roles in their daily lives and personalities.
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.
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.