Man'yōshū poem #372:

春日乎 春日山乃 高座之 御笠乃山尓 朝不離 雲居多奈引 容鳥能 間無數鳴 雲居奈須 心射左欲比 其鳥乃 片戀耳二 晝者毛 日之盡 夜者毛 夜之盡 立而居而 念曽吾為流 不相兒故荷
parupi wo/ kasuga no yama no/ takakura no/ mikasa no yama ni/ asa sarazu/ kumowi tanabiki/ kapotori no/ ma naku siba naku/ kumowi nasu/ kokoro isaywopi/ sono tori no/ katakwopwi nomwi ni/ piru pa mo/ pi no kotogoto/ yworu pa mo/ ywo no kotogoto/ tatite wite/ omopi so a ga suru/ apanu kwo yuwe ni
[On a spring day] Mount Kasuga; [The heights of] Mount Mikasa — where every morning/ the clouds cluster/ and the face-birds/ cry ceaselessly;/ like the clouds/ my heart is heavy/ like the birds/ my love unrequited;/ by day/ all day/ by night/ all night/ I stand, I sit/ I ever brood;/ for one who will not see me

That's an ugly and unpolished translation for sure, but I don't want to showcase the detail so much as the structure. Check this out:

Text		Comment
[On a Spring day]	[The heights of]	makurakotoba
Mount Kasuga	Mount Mikasa	Natural phenomena/backdrop
where every morning/ the clouds cluster	and the face-birds/ cry ceaselessly	Natural phenomena/actors + ceaselessness
like the clouds/ my heart is heavy	like the birds/ my love unrequited	Simile linking nature to self
by day/ all day	by night/ all night	Ceaselessness (intensified, almost obsessive)
I stand	I sit	Actions of self
I ever brood		Emotions of self
for one who will not see me		Reason

The poem starts out from the utterly impersonal: mountains (involved with stock epithets, no less). From there it is a jo-ha-kyū-style slowly accelerating burn through the natural actors who "inhabit" the mountains, their behavior, their behavior's relevance to the narrator, the narrator's behavior itself, a climactic and tempestuous declaration, and finally, almost as an afterthought, a placid (resigned, perhaps) explanation of why all this should be — why the poem even exists.

And all of this is presented in dual form right up until the climax of the poem, the second-last line omopi so a ga suru 念曽吾為流, a sentence which uses kakari-musubi form to emphasize the omopi, "thought (of someone)." The narrator is utterly in thrall to this omopi alone, and so it is appropriate that the A/B structure vanishes here — and note that the "tempo" of the duality has just increased, with both A and B in the same line: tatite wite.

This is the sort of thing that didn't survive when chōka ("long poems") went out of style.

Incidentally, it is no longer clear what a "face-bird" is. Maybe the cuckoo, maybe not.