It amazes me how Doma, in a span of a natural human life and without much screen time, was able to have a more than compelling character development, becoming the most rational character in the whole series. And on the other hand, we have Togata, an eternal childish character who literally only lives for the dopamine rush of watching movies, and not even at her +300 years of age could she possibly accept herself as she is. Was the author aware of it? seriously, that "revelation" was so alien and would have been out of character if it hadn't already been established how immature she is... But hey, the laughs never lacked with her, right?
Besides that blatant pandering and some plotholes here and there, it's a great manga that explores the human necessity of a clear objective in life in order to have the will to go on. I liked the touch on religion in a post-apocalyptic world and how Agni played an active role. In fact, I really liked how it appears to be a plot-driven series at first, to end up being a sick show to see how Agni reacts in every fucked up situation. Well conveyed were his emotions, that's for sure.
The ending was very fitting for the kind of history. It never tried to be your typical shonen in the first place, quite the opposite, it's an obvious satire on fighting shonens in the first half, so it's fair that it didn't focus on answer all your questions and finish with a mindfuck.