Onee-chan Activities in a Godless World is a Manga/Manhwa/Manhua in english language, REINCARNATION series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

In a world where the concept of God does not even exist, a woman as precious as a "god" has been reborn! In search of her beloved brother, Yukito, the strongest sister goes on a rampage in another world - the myth of the onee-chan has now begun!