Apex domains cannot have CNAME records.
Question and response
Question
dig int-gw.kddi.ne.jp. NS
Answer
int-gw.kddi.ne.jp. 4 NS dolphin.kddnet.ad.jp.
int-gw.kddi.ne.jp. 4 NS penguin.kddnet.ad.jp.
Authority
The response has no authority records.
Additional
dolphin.kddnet.ad.jp. 4 A 210.132.91.130
penguin.kddnet.ad.jp. 4 A 210.132.91.129
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0