Apex domains cannot have CNAME records.
Question and response
Question
dig dns.jp. NS
Answer
dns.jp. 5 NS nsa.dns.jp.
dns.jp. 5 NS nse.dns.jp.
dns.jp. 5 NS nsd.dns.jp.
dns.jp. 5 NS nsb.dns.jp.
dns.jp. 5 NS nsf.dns.jp.
dns.jp. 5 NS nsg.dns.jp.
Authority
The response has no authority records.
Additional
nsa.dns.jp. 5 A 203.119.1.4
nsb.dns.jp. 5 A 202.12.30.134
nsd.dns.jp. 5 A 210.138.175.245
nse.dns.jp. 5 A 192.50.43.153
nsf.dns.jp. 5 A 150.100.6.12
nsg.dns.jp. 5 A 203.119.40.4
nsa.dns.jp. 5 AAAA 2001:dc4:0:0:0:0:0:4
nsb.dns.jp. 5 AAAA 2001:dc2:0:0:0:0:0:2
nsd.dns.jp. 5 AAAA 2001:240:0:0:0:0:0:54
nse.dns.jp. 5 AAAA 2001:200:c000:0:0:0:0:99
nsf.dns.jp. 5 AAAA 2001:2f8:0:100:0:0:0:163
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0