One THEN/ELSE expression in the following query has a Unicode column. The query is successful and the result data type is UNICODE because the CASE expression contains 1 Unicode column and all other literals can be successfully translated to Unicode.
SELECT i, CASE WHEN i=1 THEN column_u WHEN i=2 THEN 'abc' WHEN i=3 THEN 8 WHEN i=4 THEN _KanjiSJIS'4142'XC ELSE 10 END FROM table_1 ORDER BY 1;