Apex domains cannot have CNAME records.
Question and response
Question
dig 00btm.124.178.203.in-addr.arpa. NS
Answer
00btm.124.178.203.in-addr.arpa. 5 NS ns1.mss.mind.ne.jp.
00btm.124.178.203.in-addr.arpa. 5 NS tokio.mind.ad.jp.
Authority
The response has no authority records.
Additional
tokio.mind.ad.jp. 4 A 202.228.1.36
tokio.mind.ad.jp. 4 AAAA 2001:358:31:101:0:0:0:310d
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0