Apex domains cannot have CNAME records.
Question and response
Question
dig xunit.jp. NS
Answer
xunit.jp. 4 NS ns01.xbit.jp.
xunit.jp. 4 NS ns02.xbit.jp.
Authority
The response has no authority records.
Additional
ns01.xbit.jp. 4 A 59.106.35.125
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0