Apex domains cannot have CNAME records.
Question and response
Question
dig dion.ne.jp. NS
Answer
dion.ne.jp. 4 NS dns2.dion.ne.jp.
dion.ne.jp. 4 NS ns1.neweb.ne.jp.
dion.ne.jp. 4 NS dns0.dion.ne.jp.
dion.ne.jp. 4 NS dnsa02.kddi.ne.jp.
dion.ne.jp. 4 NS dnsa01.kddi.ne.jp.
dion.ne.jp. 4 NS dns10.dion.ne.jp.
Authority
The response has no authority records.
Additional
ns1.neweb.ne.jp. 5 A 203.140.129.2
dns0.dion.ne.jp. 4 A 210.141.108.194
dns2.dion.ne.jp. 4 A 210.141.108.231
dns10.dion.ne.jp. 4 A 211.5.1.217
dnsa01.kddi.ne.jp. 5 A 54.64.39.199
dnsa02.kddi.ne.jp. 5 A 54.92.27.113
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0