Asch had just walked out of a portal, along with his Knights that Noi had created and lost his powers due to it. They are here to kill humans for their souls to bring back to Daemos.

As he walked out, they were in an alleyway. The sun was burning hot.. as well as the air felt like it was toxic for them. They were on Earth.

Back home it was always darkness with no source of sunlight. So as he got here with his Knights. And breathed in the air.. he eventually collapsed on the ground.