Hyakunin Isshu, Poem 13
Tsukuba ne no
mine yori otsuru
Minanogawa
koi zo tsumorite
fuchi to narinuru

  Like the River Mina
falling down from the peak
of Mount Tsukuba,
so my longing has grown
into a deepening pool.

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The Retired Emperor Yozei (868-949)
[Mount Tsukuba]
As time goes by, the poet's love grows deeper, like the deep pools in a river, which starts as a small trickle, but then expands into a wild stream.

The poet, Emperor Yozei (868-949), reigned from 876 to 884, as a child emperor. He was forced to abdicate by Regent Fujiwara no Mototsune and replaced by Emperor Koko, a son of Emperor Ninmyo. The histories transmit several anecdotes about Yozei's cruelty and mental instability, but these should probably be taken with a large grain of salt, for (as so often happened in Chinese and Japanese historiography) they may be fabrications to justify the forced abdication and whitewash the action by the Fujiwara powermonger.
After he had abdicated, Yozei led a very long life, and he often organized poetry gatherings. However, the present poem is the sole one with which he is represented in the imperial anthologies. In the Gosenshu anthology, this poem is accompanied by a head note reading "Sent to the Princess of the Tsuridono."

The "Princess of the Tsuridono" has been identified as Suishi, the daughter of Emperor Koko; the princess indeed did become the wife of Ex-Emperor Yozei, so this poem can be considered as ...