Apex domains cannot have CNAME records.
Question and response
Question
dig coreserver.jp. NS
Answer
coreserver.jp. 2 NS vera.ns.cloudflare.com.
coreserver.jp. 2 NS gabriel.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0