It shocked me that after how cynical the show has been, the ending was quite sincere and positive. Also shocking how despite the fact that both Satoko and Konoha continue to be pretty terrible people, it's clear that they've both made each other better, and found a really important connection with one another, and with their friends.
I can't speak for the manga but the anime feels like it has a very strong anti-nihilist sentiment by the end. Though the world that we live in is cruel, lacking entirely in justice, and forces beyond our control force us into conflict with others, it's worth it to keep living because at least we have each other, and that makes it worthy to keep on living.