Gasp! I just noticed that noone’s done ちはやぶる!
17 ちはやぶる 神代も聞かず 竜田川 からくれなゐに 水くくるとは （在原業平朝臣）
Unheard-of even since
The time of the passionate gods.
The Tatta River,
Its waters dyed
In vivid crimson.
在原業平 is his name, 朝臣 his title. He’s the son of 阿保親王 and 伊都内親王, the former of whom was a son of 平城天皇, while the latter was a daughter of 桓武天皇. Since Kanmu was also a son of Heizei, that makes Namihira both grandson and great-grandson of Heizei. Aren’t noble family trees fun? Anyway, he was not in the imperial line of succession, because his father had been banished before his birth for his involvement in Political Intrigues, so his family were made commoners, and given the name Ariwara.
For starters, ちはやぶる is a pillow word. A literal reading is something like “1000 swift swipes”, but from literary allusion, it has metaphorical reasons which range from “ferocious” to “impassionate” to “very old” to “Kamo Shrine”. Since it’s modifying 神 here, the “impassionate” meaning holds force.
The ～ず ending on 聞かず typically marks the ending of a poem - this poem uses inversion.
The 竜田川 is in modern-day Nara Prefecture. The waters of the river are dyed からかくれない, which is a shade of vivid crimson - you can see what that colour looks like here. As the book points out, in kanji it’s 唐紅, and the 唐 implies that the colour was imported from 唐の国 (= Tang Dynasty China). The poem never states what is dying the river, but this poem is typically read as being an autumn poem, making it momiji leaves or similar (and what else would it be, plus the Tatta River remains a popular autumn spot to this day).
One of the biggest tricks to this poem is in the last line - as Ye Olde Japanese didn’t have dakuten, the verb くくる could either be くくる - to tie-die - or くぐる - to go under. That is, the latter reading is that of the river flowing under a concealing blanket of fallen leaves. This leads to an alternate interpretation (one espoused by Kana in Chihayafuru), that this poem is a love poem, and the river flowing beneath the blanket of leaves represents hidden feelings of love for a woman. And indeed, Namihara is known as a bit of a romanticist, essentially a kind of Japanese Cassanova.
And also the first Chihayafuru live-action movie