Apex domains cannot have CNAME records.
Question and response
Question
dig dc2.etius.jp. NS
Answer
dc2.etius.jp. 5 NS ns3.sphere.ad.jp.
dc2.etius.jp. 5 NS ns4.sphere.ad.jp.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0