From Shaman King, a previous Ren who also had a soul partner named Bason (ignoring how their names are spelled).
Playing Gertrude: Though Gunpei is supposed to be older than Sosuke, Renn, and Saki (he even refers to himself as a man and belittles the others as being "just kids" when he steals the Engine Souls in an effort to become a Go-onger), his actor is actually younger than those of Sosuke and Renn.
However, he is indeed several years older than Saki's actress, who was, at at the time, definitely "just a kid" at 16 years of age.
Retroactive Recognition: That guy in episode 6, the one who Sosuke thought Saki was in love with? Nine years later (fittingly enough), he gets to be a Ranger himself, specifically Kyuranger'sSixth Ranger (well, twelfth, but of the three additional Rangers to the initial nine, he's the actual Sixth Ranger in function)
Too Soon: Shortly after the Go-on Wings' debut, some guy committed a murder using a dagger. As a result, the toy version of the Rocket Dagger was called Rocket Booster, and the show avoided using the word dagger for a while (as a result, the Wings would avoid calling some of their attacks).
You Look Familiar: In the final episode, Nao Oikawa appears as a customer at the bakery where Saki now works, reminding the audience eerily of Kegareshia...