Here's one possible solution:
Create a view (call it V1) that joins AFKO and RESB, using the RSNUM field. In this view pull all RESB fields and the AFKO-BUKRS field. Do not pull any other fields from AFKO.
Then in another view (say V2), do a union between V1 and AFKO. That will meet the requirement.
If you are doing all this in a calc view, then V1 would be a join node in the calc view, and V2 would be a union node taking V1 and AFKO as inputs.