Talking to Himself: In the OAV Harukanaru Toki no Naka de 2: Shiroki Ryuu no Miko both of the Fujiwara twins (Yukari-hime and Misono) are voiced by Ohtani Ikue, who voiced Fuji-hime in the first storyline. Not surprising given that both are Expies of Fuji, but since the twins are of opposite gender, the voice differs slightly depending on who is talking.
The Other Darrin: Fuji-hime was voiced by Ohtani Ikue in Ajisai Yumegatari and Hachiyou Shou. The Maihitoyo movie gave this role to Koorogi Satomi. Arguably an easy-to-do transition, given that Fuji is a ten-year-old child who would presumably have a slightly more "generic" voice than the more grown-up central cast.
As mentioned in the main article, the Hachiyou Shou anime uses a tanka poem in each episode, at the start of the ending sequence. These poems come from Kokin Wakashuu, an anthology composed during the early Heian Period (hence its use in Haruka). A list of poems used in the TV series can be retrieved from Japanese Wikipedia.
For those curious about the poem numbers in the anthology, here they are:
TV Episode 01 - #116
TV Episode 02 - #701
TV Episode 03 - #523
TV Episode 04 - #403
TV Episode 05 - #66
TV Episode 06 - #165
TV Episode 07 - #89
TV Episode 08 - #442
TV Episode 09 - #615
TV Episode 10 - #97
TV Episode 11 - #646
TV Episode 12 - #989
TV Episode 13 - #866
TV Episode 14 - #619
TV Episode 15 - #865
TV Episode 16 - #832
TV Episode 17 - #166
TV Episode 18 - #684
TV Episode 19 - #494
TV Episode 20 - #885
TV Episode 21 - #561
TV Episode 22 - #977
TV Episode 23 - #501
TV Episode 24 - #517
TV Episode 25 - #387
TV Episode 26 - #611
OAV Episode 1 - #931
OAV Episode 2 - #53
Other trivia
The theme songs for Ajisai Yumegatari and Shiroki Ryuu no Miko were sung by DASEIN. Later anime adaptations, however, started to employ voice actors from the show itself to do the opening and ending, and the credits list their respective characters' names before their actual names. For "who is who" see below:
The ending sequence for Hachiyou Shou TV, which consists of the mangaka's illustrations of the Hachiyou, normally shows the characters in the order of Seiryuu -> Suzaku -> Byakko -> Genbu. "Heaven" goes before "Earth", except for the Suzaku pair, for some reason. If the Ending Theme is replaced with a character's Image Song for Character Focus episode, however, the sequence is recut so that it starts with the Hachiyou who was the main star of the episode. For Yasuaki, who happens to be at the very end of the sequence, the order was reversed.
The title of Hachiyou Shou TV episode 23, "かわたれ" (Kawatare), is written in kanji as 彼は誰. It is an archaic term for "twilight" (akin to 黄昏 tasogare), which literally means "who is that (person)?". A particular famous scene from the episode in question employs both meanings.
The flower referenced in the manga in relation to Yasuaki's creation, kikyou (platycodon grandiflorus), isn't random — it is associated with Abe no Seimei and the Five Elements.
For reasons probably having to do with time constraints, Hachiyou Shou TV never references or explains the seal on Yasuaki's face. Simply not including the details of Yasuaki's origins (which is not even a spoiler anyway*
unless you only watched Hachiyou Shou and failed to pick on the leftover hints
) until the Internal Reveal would be one thing, but not mentioning the seal at all belongs to the Unusually Uninteresting Sight trope. As a result, they skipped over an arguably important part when the seal disappears (which would have happened during the abovementioned scene in episode 23).
Prior to Haruka 3, which started to use characters based on specific historical figures, the members of the famous clans appearing in the series — Minamoto, Fujiwara, Tachibana, Abe and Taira — had made-up given names, although many of them attempted to follow the general naming pattern prevalent in that clan.
The story involving Yorihisa and the last Nue might be a reference to the part of Heike Monogatari about Minamoto no Yorimasu killing a nue. Somewhat unfittingly, the time period in which Heike Monogatari takes place occurs much later (it was referenced eventually in Haruka 3).