Part of a
Japanese blood oath (along with the
kishomon) that some some
traditional martial arts, mostly those with their roots in the pre-Meiji era and those classified as
koryu, require initiates to sign at the time of their enrollment in a
dojo to underscore the seriousness of the their commitment to the
ryu.
The Oath usually covers rules which prevent the use of the art in an offensive way, preventing unlicensed sparring, and agreeing not to attempt to teach the art until you are avwarded the kaiden, essentially a teaching certificate. The pledge itself is not legally binding, but is considered to be a moral contract, which would only be broken by a trainee with a weak character