Shuumatsu no Sadako-san

The world has ended. Humanity isn't completely destroyed but it is a shadow of its former glory. A pair of sisters are surviving together in the ruins when they discover an ancient relic: a video. The tape is none other than Sadako's video that will curse anyone who watches it and kill them one week later. The girls are unfazed when Sadako appears since meeting another human is rare anyway. Instead, the little girls call her "Sada-chan." Sadako, meanwhile, thinks if there are more people left, she'd like to curse them. So Sadako and the two girls begin traveling together to find more people.

(Source: ANN)