Cast the Expert: Of a sort. Riku (the original Kuuga) is played by Kenji Tominaga, Kuuga's suit actor.
Fake Nationality: Jean's actor, Serugiu Vasilov, is actually from Romania, while his character is meant to be French.
Inferred Holocaust: Kuuga's Rising Mighty Kick causes a gigantic explosion, which at one point happens in a heavily urban area. This is the point in which the show begins to show that Kuuga becoming even more powerful isn't a good idea... While no one is actually killed in the blast due to Godai informing Ichijo ahead of time that his kick might be too powerful, the property damage leads the police to begin doubting No.4's status as an ally.
And then subverted: the MPD has always attempted to compensate for Kuuga's Destructive Savior aspects, and if anything everyone involved begin taking even greater steps to coordinate actions.
In Memoriam: Before the Heisei Rider era began with Kuuga's premiere, a message states that "This project is dedicated to Ishinomori-sensei". Shotaro Ishinomori was the creator of the Kamen Rider series, and Kuuga was an idea he had to revive before his death.
Old Shame: Averted. A long-standing rumor claimed that Joe Odagiri resented his time on Kuuga and even had it taken off of his resumé after he moved on to more serious roles. However, this came about due to a mistranslated interview (what he actually said was that he didn't want to be Typecast as a kids' show actor), and there's far more corroborating evidence to show that he's at least neutral on the role: He kept in touch with his co-stars, gave a speech at Wakana Aoi (the actress who played Yusuke's sister Minori)'s wedding, and was committed to doing The Movie up until its eventual cancellation. When asked directly about changing his resumé, Odagiri even said "I didn't do that! Don't say such terrible things!". However, it does seem that Odagiri doesn't care for Tokusatsu in general and mostly took the role as a favor to the producer; since that producer was fired following the disastrous production of Kamen Rider Hibiki, he has little to no motivation to ever reprise his role.
There was supposed to be a theatrical film set after the events of the TV series, but the project languished in development hell when the writers couldn't come up with a satisfactory way to continue the story and the production was eventually canceled in 2006, making Kuuga the only Heisei series without a theatrical movie.
The early designs for Ultimate Kuuga had a much more regal (and gold) aesthetic. These would end up influencing the design of Rising Ultimate Form in Decade.
Masaya Matsukaze auditioned for the title role, but was ultimately passed over for Joe Odagiri. Considering he's been in multiple Super Sentai series, it's easy to imagine that Matsukaze would have been far more willing to reprise his role in later productions than Odagiri.