% APNIC found the following authoritative answer from: whois.apnic.net

% [whois.apnic.net]
% Whois data copyright terms    http://www.apnic.net/db/dbcopyright.html

% Information related to '2400:2600::/23'

% Abuse contact for '2400:2600::/23' is 'abuse@bbix.net'

inet6num:       2400:2600::/23
netname:        BBIX-IPv6-20110804
descr:          BBIX IPv6 Network
descr:          Email address for spam or abuse complaints : abuse@bbix.net
country:        JP
admin-c:        SA421-AP
tech-c:         SA421-AP
status:         ALLOCATED NON-PORTABLE
mnt-by:         MAINT-JP-BBTECH
mnt-lower:      MAINT-JP-BBTECH
mnt-routes:     MAINT-JP-BBTECH
mnt-irt:        IRT-BBIX-JP
last-modified:  2011-08-25T06:47:29Z
source:         APNIC

irt:            IRT-BBIX-JP
address:        Tokyo Shiodome bldg.,
address:        1-9-1, Higashi-Shimbashi
address:        Minatoku,Tokyo, Japan
e-mail:         abuse@bbix.net
abuse-mailbox:  abuse@bbix.net
admin-c:        SN936-AP
tech-c:         SN936-AP
tech-c:         SN936-AP
auth:           # Filtered
remarks:        abuse@bbix.net is invalid
mnt-by:         MAINT-JP-BBTECH
last-modified:  2024-08-28T13:11:51Z
source:         APNIC

role:           SoftbankBB ABUSE
address:        Tokyo Portcity Takeshiba Office Tower 22F,  1-7-1, Kaigan, Minatoku,Tokyo
country:        JP
phone:          +81-3-6688-5120
e-mail:         abuse@e.softbank.co.jp
remarks:        Please send spam report,virus alart
remarks:        or any other abuse report
remarks:        to  abuse@e.softbank.co.jp
remarks:        Any other Information, Notice,
remarks:        Please send to hostmaster@bbtec.net
admin-c:        KF291-AP
tech-c:         KF291-AP
nic-hdl:        SA421-AP
mnt-by:         MAINT-JP-BBTECH
last-modified:  2024-03-26T02:44:48Z
source:         APNIC

% This query was served by the APNIC Whois Service version 1.88.25 (WHOIS-AU3)

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