Not just their honor, honor in general.
Never heard of
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? Him and his family lived in disgrace for near to 90 years because he survived Titanic sinking ; this partly due to the way it was, falsely depicted at first. Everyone, from the government to the public, passing by the press, was against him for his supposed dishonor. And they were against him because, at this time, in their eyes it was a dishonor for the whole nation.
So yeah, to answer OP, make him loose his honor. Even nowadays there's nothing more humiliating for a Japanese man. But obviously, he can't be something simple, there's degrees, even in dishonor.
The Hosono's story could be a solution here, everything depend of the reason why you want to humiliate him. If it's for a global reason, as background for the story by example, a powerful opponent can perfectly have led, through the press, a successful defamation campaign against him. On a smaller scale, the rights rumors spread to the right persons can quickly lead to the whole neighborhood believing some dishonorable act that he would have done.
Be noted that in both cases, it's a risky move. If the defamation campaign is uncovered, its author will be highly dishonored, because it would mean that the defamer is too coward to face his opponent.
