Apex domains cannot have CNAME records.
Question and response
Question
dig 250.110.133.static.iijgio.jp. NS
Answer
250.110.133.static.iijgio.jp. 5 NS ns00.iij-dns.net.
250.110.133.static.iijgio.jp. 5 NS ns01.iij-dns.jp.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0