classic waka stream

I do not know where
we shall meet—but these traces
I write and leave here
on the seaweed of this shore,
look on them as a keepsake

Meaning
I do not know where we shall meet again; but look on these traces I write and leave behind as a keepsake.
Commentary
Volume Ten: The Parading of the Heads

　On the seventh of the second month of the third year of Juei the Taira were beaten at Ichi-no-tani, and on the twelfth the heads of the dead came into the capital. Everyone connected with the house grieved, wondering what would fall on them next. Koremori's wife could hardly breathe for fear that her husband's head was among those hung at the prison gate.
　What she felt could not fail to reach Koremori across the sea. Recovering from illness at Yashima, he was thinking of his wife and children too. How anxious they must be, he said; even if my head is not there they will imagine me drowned or shot; they may believe I am no longer in the world at all. Let them at least know that I am barely alive. He fitted out a messenger and wrote three letters to send to his wife in the capital.
　When I think of you among enemies, a woman alone with two children, my heart flies straight back to the sky over the capital. I would give anything to bring the three of you here and live as a family of four; but this place will not stay safe either, and if it were only my own hardship I would bear anything—to put the three of you through such misery I could not do, and so I have given up the thought. At the end of this letter, written with unending longing, stood a poem. This is it.
　To the children he wrote separately: I think of nothing but how you pass your days; I mean to bring you to your father soon, so look forward to that, take care of your mother, and wait.

　Moshiogusa is the seaweed gathered for salt-burning, and in poetry it introduces kaki, "to write." He makes his own letter that seaweed—a man on the shore at Yashima naming his letter with the objects of the shore.
　The se of ōse, "meeting," belongs to water as well, so that seaweed, meeting, and kaki—raking and writing at once—build the whole verse out of a single stretch of coast.
　The point is katami, keepsake: what a dead man leaves behind. For a living man to call his own letter a keepsake is to have decided that he will not return. To his children he wrote that he would send for them; to his wife he wrote "keepsake." The distinction is deliberate.
　Koremori will slip away from Yashima, take vows at Kōya, make the Kumano pilgrimage, and drown himself off Nachi. This poem is where that decision first takes the form of words.

izuku to mo shiranu……not knowing where.
ōse……a meeting; se also means a shallows, belonging to water imagery.
moshiogusa……seaweed gathered for salt-burning; introduces "to write."
kakioku……to write and leave behind; puns on "to rake."
ato……traces; handwriting.
katami……a keepsake, especially one left by the dead.
Koremori……son of Shigemori and grandson of Kiyomori.
Yashima……the Taira base in Sanuki province.
gokumon……the prison gate where heads were displayed.
wago……a respectful term for someone's son.
Source
Heike Monogatari
Other