Apex domains cannot have CNAME records.
Question and response
Question
dig air.ne.jp. NS
Answer
air.ne.jp. 5 NS ns3.air.ne.jp.
air.ne.jp. 5 NS ns2.air.ne.jp.
air.ne.jp. 5 NS ns1.air.ne.jp.
air.ne.jp. 5 NS pns.air.ne.jp.
Authority
The response has no authority records.
Additional
ns1.air.ne.jp. 5 A 210.166.77.200
ns2.air.ne.jp. 5 A 210.159.75.200
ns3.air.ne.jp. 5 A 210.166.92.200
pns.air.ne.jp. 5 A 210.166.77.251
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0