In today's dictionaries, 比翼連理 is a figure for a husband and wife, or a man and a woman, who are close. It also stands for the deep pledge between them. The four characters say paired wings, joined grain. 比翼 is a legendary bird that does not fly unless paired, and 連理 is two trees whose wood has grown into one.
In a tale from the Muromachi or early Edo period, Urashima Tarō's bride asks him for the pledge of husband and wife, and he agrees. In their talk they say, in heaven let us be the wing-paired bird, on earth the branch of one grain. A manual for the newly married, from 1940, explains 比翼連理 as husband and wife, once strangers, ending up as one.
The four characters are a short form of a couplet in Bai Juyi 白居易's 長恨歌 of 806, 在天願作比翼鳥 在地願爲連理枝, which set two older images side by side: the wing-paired bird of the Chinese 爾雅, and the tree of joined grain, an omen of good rule before it was a love word. In Japanese they stand together in 三善清行's 善家秘記 of the early tenth century, as the 扶桑略記 quotes it; the 日国's earliest example is the 吾妻鏡's entry for 1202.
We want you to be as happy with the meaning as you are with Master Takase's art. To learn more, visit Philology of 比翼連理.