Apex domains cannot have CNAME records.
Question and response
Question
dig A160.183.249.210.in-addr.arpa. NS
Answer
A160.183.249.210.in-addr.arpa. 5 NS ns01.pwd.ne.jp.
A160.183.249.210.in-addr.arpa. 5 NS jens01.siterock.co.jp.
A160.183.249.210.in-addr.arpa. 5 NS ttnet01.siterock.co.jp.
Authority
The response has no authority records.
Additional
ns01.pwd.ne.jp. 4 A 211.10.246.214
jens01.siterock.co.jp. 5 A 202.33.115.2
ttnet01.siterock.co.jp. 5 A 210.249.183.162
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0