The term Rikombyō is composed with the word rikon, signifying a "shade," "ghost," or "spectre," and the word byō, signifying "sickness," "disease." An almost literal rendering would be "ghost-sickness." In Japanese-English dictionaries you will find the meaning of Rikombyō given as "hypochondria;" and doctors really use the term in this modern sense. But the ancient meaning was a disorder of the mind which produced a Double; and there is a whole strange literature about this weird disease. It used to be supposed, both in China and Japan, that under the influence of intense grief or longing, caused by love, the spirit of the suffering person would create a Double. Thus the victim of Rikombyō would appear to have two bodies, exactly alike; and one of these bodies would go to join the absent beloved, while the other remained at home. (In my "Exotics and Retrospectives," under the title "A Question in the Zen Texts," the reader will find a typical Chinese story on the subject,—the story of the girl Ts'ing.) Some form of the primitive belief in doubles and wraiths probably exists in every part of the world; but this Far Eastern variety is of peculiar interest because the double is supposed to be caused by love, and the subjects of the affliction to belong to the gentler sex.... The term Rikombyō seems to be applied to the apparition as well as to the mental disorder supposed to produce the apparition: it signifies "doppelgänger" as well as "ghost-disease."
—With these necessary explanations, the quality of the following kyōka can be understood. A picture which appears in the Kyōka Hyaku-Monogatari shows a maid-servant anxious to offer a cup of tea to her mistress,—a victim of the "ghost-sickness." The servant cannot distinguish between the original and the apparitional shapes before her; and the difficulties of the situation are suggested in the first of the kyōka which I have translated:—
Ko-ya, soré to?
Ayamé mo wakanu
Rikombyō:
Izuré we tsuma to
Hiku zo wazuraü!
[Which one is this?—which one is that? Between the two shapes of the Rikombyō it is not possible to distinguish. To find out which is the real wife—that will be an affliction of spirit indeed!]