Apex domains cannot have CNAME records.
Question and response
Question
dig ocs.nricloud.jp. NS
Answer
ocs.nricloud.jp. 2 NS ns1.p200.dns.ap-dcc-tokyo-1.oci.nricloud-realm.jp.
ocs.nricloud.jp. 2 NS ns3.p200.dns.ap-dcc-tokyo-1.oci.nricloud-realm.jp.
ocs.nricloud.jp. 2 NS ns5.p200.dns.ap-dcc-tokyo-1.oci.nricloud-realm.jp.
ocs.nricloud.jp. 2 NS ns4.p200.dns.ap-dcc-tokyo-1.oci.nricloud-realm.jp.
ocs.nricloud.jp. 2 NS ns2.p200.dns.ap-dcc-tokyo-1.oci.nricloud-realm.jp.
ocs.nricloud.jp. 2 NS ns6.p200.dns.ap-dcc-tokyo-1.oci.nricloud-realm.jp.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0