classic waka stream

crane and tortoise too
know not what lies beyond a thousand years—
so to my heart
that cannot ever be content
I yield, and let it reach the end

Meaning
Even the crane and the tortoise do not know what lies beyond a thousand years, yet I yield to my heart that cannot be content, and let it go on to the end.
Commentary
Book Seven Felicitations

A poem composed at the sixtieth-year celebration of Fujiwara no Miyoshi.

Though the crane and tortoise are symbols of long life, even they do not know what comes beyond a thousand years. The poet, unable to be satisfied even with such longevity, entrusts everything to an unfulfilled heart, expressing the wish that the addressee’s long life may continue without end.

"Akanu kokoro” means a heart that cannot be satisfied, and depending on whose heart it refers to, the nuance may vary. If it is the recipient’s heart, it suggests a wish that they may live on until they themselves are content.

A note in the text adds that some attribute this poem to Fujiwara no Tokiharu.
Author
Shigeharu Fujiwara
Source
Kokin Wakashu
Other