The "Subject" and "FileName" field in Advanced Threat Protection (ATP) Manager or Symantec Endpoint Detection and Response (SEDR) Manager > Search > Database > Events > Email Malicious events are not MIME decoded for Japanese characters and are not correctly displayed,
Symantec is aware of this issue and a fix will be provided in a future release of SEDR or ATP:Email service
This document will be updated with the information when confirmed.