Apex domains cannot have CNAME records.
Question and response
Question
dig ams.vectant.ad.jp. NS
Answer
ams.vectant.ad.jp. 5 NS ns2.vectant.ne.jp.
ams.vectant.ad.jp. 5 NS ns1.vectant.ne.jp.
Authority
The response has no authority records.
Additional
ns1.vectant.ne.jp. 4 A 163.139.230.164
ns2.vectant.ne.jp. 4 A 163.139.230.165
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0