Apex domains cannot have CNAME records.
Question and response
Question
dig aichi.ocn.ne.jp. NS
Answer
aichi.ocn.ne.jp. 3 NS ns-tk041.ocn.ad.jp.
aichi.ocn.ne.jp. 3 NS ns-os041.ocn.ad.jp.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0