Shuumatsu no Majo to Ningyou

In the near future, civilization has collapsed due to war and natural disasters, on the verge of full-blown apocalypse. Zoe, a young police-woman who struggles to maintain order, fights off the local mafia to save an elderly woman. But then the mafia releases a giant robot weapon to pursue them… Meanwhile, it seems like the old woman also has secrets of her own......?

(Source: Comic Border, translated)