Apex domains cannot have CNAME records.
Question and response
Question
dig sa.crosshead.jp. NS
Answer
sa.crosshead.jp. 5 NS ns-1641.awsdns-13.co.uk.
sa.crosshead.jp. 5 NS ns-647.awsdns-16.net.
sa.crosshead.jp. 5 NS ns-163.awsdns-20.com.
sa.crosshead.jp. 5 NS ns-1418.awsdns-49.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0