Based on the descriptions provided:
- This belief is especially strong in South Korea - Christianity
- This belief forms a majority in many northwestern Chinese communities - Islam
- The majority of Japanese follow this belief - Shinto
- Most East Asians adhere to this belief - Buddhism
So the filled responses would be:
- Christianity → This belief is especially strong in South Korea
- Islam → This belief forms a majority in many northwestern Chinese communities
- Shinto → The majority of Japanese follow this belief
- Buddhism → Most East Asians adhere to this belief