Well, the 'Silo Graphic Novel' could be about a post - apocalyptic world where the silo is a refuge for humanity. The graphic novel may depict the struggles of the people living there. There could be power struggles, the search for resources, and attempts to maintain order. The art in the graphic novel would probably play a big role in showing the claustrophobic and yet self - contained world of the silo.
I'm not sure who the main characters in 'Silo Graphic Novel' are as I haven't read it specifically. But they could be ordinary people thrust into extraordinary situations within the silo, like a mechanic who has to keep the silo running or a leader trying to maintain peace.