Apex domains cannot have CNAME records.
Question and response
Question
dig cloud-mail.jp. NS
Answer
CLOUD-MAIL.JP. 4 NS NS22.FreeBit.NET.
CLOUD-MAIL.JP. 4 NS NS21.FreeBit.NET.
Authority
The response has no authority records.
Additional
ns21.freebit.net. 4 A 61.195.7.21
ns22.freebit.net. 4 A 61.195.7.22
ns21.freebit.net. 4 AAAA 2001:3e0:0:61:0:0:53:21
ns22.freebit.net. 4 AAAA 2001:3e0:0:61:0:0:53:22
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0