Apex domains cannot have CNAME records.
Question and response
Question
dig 128.137.154.210.in-addr.arpa. NS
Answer
128.137.154.210.in-addr.arpa. 4 NS rx7.mazda.co.jp.
128.137.154.210.in-addr.arpa. 4 NS ns-tk012.ocn.ad.jp.
128.137.154.210.in-addr.arpa. 4 NS ns2.mazda.co.jp.
Authority
The response has no authority records.
Additional
rx7.mazda.co.jp. 4 A 210.154.137.152
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0