Apex domains cannot have CNAME records.
Question and response
Question
dig lux.jp-east-2.compute.idcfcloud.net. NS
Answer
lux.jp-east-2.compute.idcfcloud.net. 3 NS ns03.idcfcloud.com.
lux.jp-east-2.compute.idcfcloud.net. 3 NS ns01.idcfcloud.com.
lux.jp-east-2.compute.idcfcloud.net. 3 NS ns02.idcfcloud.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0