mx.willap.jp has no NS records.
NS records for this zone are defined at willap.jp.
NS records for this zone are defined at willap.jp.
Question and response
Question
dig mx.willap.jp. NS
Answer
The response has no answer records.
Authority
willap.jp. 900 SOA ns-1862.awsdns-40.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0