Nagaraeba omoide ni semu omoiideyo kimi to Mikasa no yama no ha no tsuki - Shika Wakashu(English Translation & Meaning)

長らへば思ひ出にせむ思ひ出でよ
君とみかさの山の端の月

Roma-ji: Nagaraeba omoide ni semu omoiideyo kimi to Mikasa no yama no ha no tsuki
English Translation: If I live on long,
I shall keep it as a memory —
remember it too:
the moon we saw together
at the rim of Mount Mikasa
Meaning: If I live on, I will keep it as a memory; and you, too, remember it — the moon over the ridge of Mount Mikasa that we saw together.
Commentary: Book Nine Miscellaneous Poems I 306

If he lives on, the poet will cherish this night's moon as a memory, and he asks his companion to remember too the moon they saw together over Mount Mikasa. Playing "mi" (to see) against Mikasa, the poem conveys a quiet wish to keep the moon they shared as a token after parting.

The first line, "nagaraeba," is a hypothetical with the irrealis and "ba": if I live on.
The second line, "omoide ni semu," uses the volitional "mu": I will make it a memory. It has eight syllables, an extra-syllable line, with a break after the second line.
The third line, "omoiideyo," calls on the other in the imperative to remember, with a break after the third line. It repeats "omoide" from the second line.
The fourth line, "kimi to Mikasa no," is a pivot word joining "mi" (seen with you) and Mikasa, a poetic place in Yamato Province. Poems 291 and 335 of this book also sing of Mount Mikasa.
The final line, "yama no ha no tsuki," ends with a noun, presenting the moon on the ridge of Mount Mikasa.
Source: Shika Wakashu
Prev Poem: Tsuki ni koso mukashi no koto wa oboekere ware o wasururu hito ni misebaya
Next Poem: Ōsaka no seki no sugihara shita harete tsuki no moru ni zo makasetarikeru