IRL Manhattan Cafe had a son with Yukino Bijin. No name was registered for the horse though and he pretty much faded into obscurity without racing.
In-game, Cafe is roommates with Yukino. Cafe is implied to be fond of her, judging by how Cafe describes their interactions.
IRL Gold City has no relation with Yukino Bijin.
Uma!Yukino looks up to Gold City because she sees the latter as a model "city girl" whom she wishes to emulate. Gold City meanwhile is taken by Yukino's countryside girl-esque "unadorned purity".
There is another IRL Gold City (a gelding, no relation to the other Gold City) who was transferred from JRA Central to the Iwate regional horse races, mirroring the opposite of Yukino (who was transferred from Iwate to JRA Central. This may be a partial inspiration for the in-game Yukino/City relationship.
Burube
Yebe
Slang abbreviation for "blue base" and "yellow base", used to indicate whether someone's skin tends more towards bluer or yellower shades, for the purposes of color coordination when picking clothes.
To someone unacquainted (like Yukino here), it sounds like "blueberry" and "house beh".
