Apex domains cannot have CNAME records.
Question and response
Question
dig area51c.commufa.jp. NS
Answer
area51c.commufa.jp. 5 NS dns2.commufa.jp.
area51c.commufa.jp. 5 NS dns1.commufa.jp.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0