“TVTropes: Mobile Suit Gundam: Char’s Counterattack”, 2019 (; backlinks; similar):
Mobile Suit Gundam: Char’s Counterattack is the first full-length Gundam animated movie released in 1988. Char’s Counterattack is the culmination of the original saga begun in Mobile Suit Gundam and continued through Mobile Suit Zeta Gundam and Mobile Suit Gundam ZZ, marking the final conflict of the fourteen-year rivalry between Amuro Ray and Char Aznable, and the end of the Earth Federation/Zeon conflicts.
…The movie is noteworthy for having a rather unusual genesis. Originally, director Yoshiyuki Tomino was going to wrap up Amuro and Char’s storyline in Gundam ZZ, but mid-way through production he was given the go-ahead to make a movie, forcing the plot of ZZ to be rewritten (details on its trope page). In the meantime Tomino wrote the novel Hi-Streamer, but when Sunrise gave him the green light, he went back and wrote a second novel, Beltorchika’s Children, which he specifically wrote to be adapted into a movie. However, Sunrise instead chose to use Hi-Streamer, with the final film being a pretty straightforward adaptation of its second half.