Apex domains cannot have CNAME records.
Question and response
Question
dig ocn.ad.jp. NS
Answer
ocn.ad.jp. 5 NS ns2.ocn.ad.jp.
ocn.ad.jp. 5 NS ns1.ocn.ad.jp.
Authority
The response has no authority records.
Additional
ns1.ocn.ad.jp. 5 A 202.234.232.202
ns2.ocn.ad.jp. 5 A 211.129.12.204
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0