Religion in World I-X

There has always been religion on all the worlds in World I-X.

Christianity
Christianity was founded on World I. It is the largest religion in World I. In 1988, with the first exploration of World II, some explorers brought the Christian religion with them. However, it never became one of the largest religions on an other world than World I.

Islam
Islam is the second largest religion on World I.

Vendranism
Vendranism is the largest religion on World IV.