Apex domains cannot have CNAME records.
Question and response
Question
dig 232.115.33.202.in-addr.arpa. NS
Answer
232.115.33.202.in-addr.arpa. 3 NS ns.spin.ad.jp.
232.115.33.202.in-addr.arpa. 3 NS jens01.siterock.co.jp.
232.115.33.202.in-addr.arpa. 3 NS ns.tokyo.spin.ad.jp.
232.115.33.202.in-addr.arpa. 3 NS ttnet01.siterock.co.jp.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0