Apex domains cannot have CNAME records.
Question and response
Question
dig aws.pi-pe.co.jp. NS
Answer
aws.pi-pe.co.jp. 5 NS ns-1633.awsdns-12.co.uk.
aws.pi-pe.co.jp. 5 NS ns-995.awsdns-60.net.
aws.pi-pe.co.jp. 5 NS ns-313.awsdns-39.com.
aws.pi-pe.co.jp. 5 NS ns-1388.awsdns-45.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0