ns5.xserver.jp has no CNAME records.
Question and response
Question
dig ns5.xserver.jp. NS
Answer
The response has no answer records.
Authority
xserver.jp. 900 SOA ns1.xserver.jp. root.sv0.xserver.jp. 0 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0