The Horizon - Episode 1
m.webtoons.com
An apocalyptic event has wiped out most of the population. A young boy meets a girl in the sea of dead bodies. Bound together by their shared trauma, they keep walking forward in hopes of finding a safe haven. But does a safe haven exist in a world that has lost its humanity?

It is badly censored in Webtoon, I would suggest looking for the uncensored version.