Apex domains cannot have CNAME records.
Question and response
Question
dig bserver.jp. NS
Answer
bserver.jp. 4 NS ns-1963.awsdns-53.co.uk.
bserver.jp. 4 NS ns-706.awsdns-24.net.
bserver.jp. 4 NS ns-353.awsdns-44.com.
bserver.jp. 4 NS ns-1457.awsdns-54.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0