Apex domains cannot have CNAME records.
Question and response
Question
dig 5.d-53.jp. NS
Answer
5.d-53.jp. 5 NS ns.iij-dns.jp.
5.d-53.jp. 5 NS ns.iij-dns.biz.
5.d-53.jp. 5 NS ns.iij-dns.net.
Authority
The response has no authority records.
Additional
ns.iij-dns.biz. 4 A 202.32.219.52
ns.iij-dns.net. 4 A 210.138.20.112
ns.iij-dns.biz. 4 AAAA 2001:240:bb81:0:0:0:28:52
ns.iij-dns.net. 4 AAAA 2001:240:bb81:0:0:0:29:112
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0