This is the first Sailor Moon film to be released in 26 years following Sailor Moon SuperS: O Buraco Negro dos Sonhos (1995) which was part of the original anime release.
This film is supposed to adapt the Sailor Moon SuperS series to the two films. It is an extension of Sailor Moon Crystal. It was supposed to be released right after the Olympics 2020 in Japan, but because of the Coronavirus quarantine pushing the summer Olympics to 2021. Both parts where then aired in January and February 2021 respectively. This is also Sailor Saturn's first appearance in a movie, as she was the only main Sailor Soldier not to appear in a movie during the original anime.
Unlike its predecessor Sailor Moon Crystal (2014) which debuted on streaming sites like Hulu and Crunchyroll, both movies will instead debut on Netflix in June 2021 for its initial English release distribution. In addition it would be around a month after Eternal's release that Netflix would also get the streaming rights to Crystal as well.
Unlike the original anime, the Outer Sailor Soldiers take action against the Dead Moon Circus which was part of the original manga. In the original 90's anime version of SuperS the Outer Sailor Soldiers did not appear during the main episodes of that season. Instead in the original anime, when Queen Nehelenia later returned at the beginning of the Stars season in a story which is partly filler, that was when the Outer Sailor Soldiers got involved.
This is Officially Sailor Moon's Longest Film as the other Sailor Moon Films Clocked in just 60 Minutes