[Den-O]

Well at the time it was an actual farewell, it was all that was planned. The reason Takeru Satou doesn't play Ryutaro in the Decade crossover movie is because they never originally planned to do more Den-O (and he's never returned since because of his involvement playing Kenshin Himura). But the popularity was clear for that franchise so they had to do more. They shoe-horn in that whole "the timeline has been changed" nonsense so that they can use the kid who played young Ryutaro from Ore Tanjou. Still a good movie but Final Countdown was easily the peak of the Den-O franchise. The final fight that includes all the Taros in their Den-O forms with Zeronos taking on all the baddies was just ridiculously epic.