Apex domains cannot have CNAME records.
Question and response
Question
dig rakus-infra.jp. NS
Answer
rakus-infra.jp. 5 NS ns-598.awsdns-10.net.
rakus-infra.jp. 5 NS ns-1113.awsdns-11.org.
rakus-infra.jp. 5 NS ns-1892.awsdns-44.co.uk.
rakus-infra.jp. 5 NS ns-226.awsdns-28.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0