the world starts to heat up so much that the sky is left permanently bright outside if i remember correctly, most likely due to the overuse of electrical supplies, so much so that everything starts to fall apart as people chaotically turn to Hikaro to survive. more and more people start to die due to the heat, exceeding the chaos.
in this manga, from how i see it, "Mokumoku Man" represents hope. he is a symbol of hope, especially demonstrated through Minazo and the little monologue at the end of the manga—how one's hope can truly be anything. that's how it was for Minazo and Shishio, as they both clung to Mokumoku Man to survive. Shishio clings to Mokumoku Man to cover his grief, while Minazo does so to cover his feelings of loneliness. Minazo and Shishio are two sides of the same coin: one who prays (hopes) for himself, and one who prays for the sake of others. the selfish and the selfless indeed.