Apex domains cannot have CNAME records.
Question and response
Question
dig 61.226.202.in-addr.arpa. NS
Answer
61.226.202.in-addr.arpa. 4 NS ns2.inetidc.jp.
61.226.202.in-addr.arpa. 4 NS ns1.inetidc.jp.
Authority
The response has no authority records.
Additional
ns1.inetidc.jp. 4 A 61.196.168.229
ns2.inetidc.jp. 4 A 61.196.169.5
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0