Apex domains cannot have CNAME records.
Question and response
Question
dig fence-mail.jp. NS
Answer
fence-mail.jp. 4 NS ns0.dns.nifcloud.com.
fence-mail.jp. 4 NS ns1.dns.nifcloud.com.
Authority
The response has no authority records.
Additional
ns0.dns.nifcloud.com. 4 A 116.83.160.1
ns1.dns.nifcloud.com. 4 A 116.83.164.1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0