Apex domains cannot have CNAME records.
Question and response
Question
dig ote.kddi.com. NS
Answer
ote.kddi.com. 4 NS ns-300.awsdns-37.com.
ote.kddi.com. 4 NS ns-555.awsdns-05.net.
ote.kddi.com. 4 NS ns-1216.awsdns-24.org.
ote.kddi.com. 4 NS ns-2026.awsdns-61.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0