The Marriage Registration's Password (Part 1)

When Yumi sees a news story about the shogi championship match, she learns for the first time that Haneda is a professional shogi player. Several years earlier, Yumi received an envelope from Haneda and was instructed not to open it until he had acquired "all seven." Haneda has now won all seven major shogi titles. Detective Sato reasons that the envelope's contents must be a marriage registration, but Yumi threw out the magazine she kept the envelope in that morning. They immediately head to the dump site, but the magazine is gone. Conan and the Detective Boys attempt to help Yumi find the envelope, but...