Japan: Unsigned contract, client refuses to pay.

I submitted a contract to a client for review and began work on the project
as requested--I'm an executive search consultant and the client asked me to submit candidate resumes for hiring consideration.

I introduced a candidate in January that the client then declined for
consideration; later (last week) I found out that they did indeed meet and
hire the candidate to start in March, due to another recruiting agency which
initiated contact with the client about the candidate the day After my
introduction. This is documented in emails, including the client's
admission that the other agent changed his mind regarding the candidate, and that as he did not sign my search agreement, he felt no obligation to pay me.

I should point out that the client did not inform me that they wished Not to
work with me--they did, in fact, acknowledge receipt of my search agreement and asked for resume submissions. My agreement has no time limit on introductions, although some agencies have one or two year time limits. In this case, the candidate was hired within 2 months of my introduction.

Precedent in Japan in the past has shown that even without a signed contract
(which the client argues is key) I would win such a case in court: the
first agent to introduce a candidate has rights to payment. The firm I work
in did indeed take a large MNC to court about 6 years ago in a like situation and won. In this case, I can demonstrate that we were engaged in ongoing business by my introducing candidates to the client, though without a signed search agreement in place.

The laws may have changed, however, so I am not sure if I can resort to
legal methods (ie. Tokyo district court), if negotiation with the client
fails.

Have you any advice or insight into this? Thank you.
-BB.