The coldest line in the Man’yōshū isn’t actually in a poem. It’s in the note about the author that comes afterwards. Here it is with the poem for context; this is MYS 8/1428, in a “Spring: Miscellaneous” section. Original orthography taken from Man’yōshū kensaku, the latest iteration of the venerable MYS search system from Yamaguchi University.
忍照 難波乎過而 打靡 草香乃山乎 暮晩尓 吾越来者 山毛世尓 咲有馬酔木乃 不悪 君乎何時 徃而早将見
(ositeru / nanipa wo sugwite / uti-nabiku / kusaka no yama wo / yupugure ni / wa ga kwoye-kureba / yama mo se ni / sakyeru asibi no / asikaranu / kimi wo itu si ka / yukite paya mimu)
The content is fairly unremarkable:
One poem about Mount Kusaka [part of Mount Ikoma]
Passing Oshiteru [Cranston suggests “[of the] Shining Waves”] Naniwa, Mount Kusaka I cross as evening falls; crowding the mountain in bloom, the ashibi (Japanese andromeda) are not bad; when shall I arrive and see not-bad you next?
The first two thirds of the poem are all leading up to asikaranu (not bad), which puns on asibi (modern ashibi or asebi, and functions as a pivot to get us from the vivid but objective description of the journey to the inner thoughts of the journeyer. Who indeed has not longed for their not-bad beloved after extended separation?
(Since the actual text of the source is just 不悪, i.e. not represented phonemically, some people use another reading of 悪 to render the relevant word nikukaranu [“not loathsome”], but this doesn’t really do it for me.)
Moving on, here’s the note about the author:
The author of the preceding poem being of low status, their name is omitted
Not “unknown,” but “omitted.” Intentionally. I guess this is what happens when your commitments to literary meritocracy and aristocracy conflict. I’m sure the poet was promised a lot of exposure, though.
(According to Satake Akihiro et al, who edited the Shin Nihon koten bungaku taikei 新日本古典文学大系 edition of the MYS, this is the only such note in the collection.