Apex domains cannot have CNAME records.
Question and response
Question
dig 0.7.175.210.in-addr.arpa. NS
Answer
0.7.175.210.in-addr.arpa. 5 NS ns2.inetidc.jp.
0.7.175.210.in-addr.arpa. 5 NS ns1.inetidc.jp.
Authority
The response has no authority records.
Additional
ns1.inetidc.jp. 5 A 61.196.168.229
ns2.inetidc.jp. 5 A 61.196.169.5
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0