Apex domains cannot have CNAME records.
Question and response
Question
dig mexne.jp. NS
Answer
mexne.jp. 4 NS ns0.mexne.jp.
mexne.jp. 4 NS ns1.mexne.jp.
Authority
The response has no authority records.
Additional
ns0.mexne.jp. 4 A 210.155.128.28
ns1.mexne.jp. 4 A 210.155.128.51
ns0.mexne.jp. 4 AAAA 2001:2f0:0:2:0:0:0:28
ns1.mexne.jp. 4 AAAA 2001:2f0:0:1:0:0:0:51
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0