It's been a long wait, but after the third season of Sailor Moon Crystal came to a close in 2016, Toei opted to adapt the fourth arc of the Sailor Moon manga as two feature-length movies called Sailor Moon Eternal. The first of the two films is set for release on January 8, 2021 in Japan.
As fans already know, these movies will cover the fourth major story arc in the manga: Dream. The new enemy is the Dead Moon Circus and they are after the elusive and mysterious Golden Crystal that resides somewhere on Earth. Dream was loosely adapted in the 1990s Sailor Moon anime as the fourth season, SuperS. However, the plot diverged so much from the source material that this new adaptation will inevitably feel so different, not to mention more faithful to manga creator Naoko Takeuchi's vision.
The Outers Will Be Present
Unlike in SuperS, the Outers will be present for the majority of the Dead Moon story. It's true Uranus and Neptune appeared in a self-contained segment in the SuperS special, but other than that, they didn't come in contact with the other Sailor Guardians. In Dream, the four Outer Guardians play a significant role in the fight against Nehalennia.
It's not clear if the Outers will be in the first Eternal movie, but they will definitely appear somewhere in the duology.
Chibi-Usa and Usagi Will Switch Ages
The '90s anime indeed adapted the manga subplot where Usagi and Chibi-Usa switch ages all thanks to PallaPalla. So of course Eternal, which continues what Crystal began, will include the age swap, as well. Unlike in SuperS, though, the incident occurs sooner than later, and the remedy is tied directly to their new powers rather than having Pegasus undo the spell like he did in the classic anime.
The Amazon Trio Will Have a Reduced Role
In the manga, the Amazon Trio were created by the Amazoness Quartet and were essentially one-off villains. Whereas in SuperS, the three troublesome characters — Hawk's Eye, Tiger's Eye, Fisheye — had more significant roles and appeared in multiple episodes before being redeemed. The '90s anime habitually expanded upon evil characters who didn't have as much presence in the manga.
The Amazoness Quartet conjured the Trio from animals and then sent them after Sailor Mercury, Sailor Mars, and Sailor Jupiter.
Sailor Mars' Familiars Will Take On Human Forms
Rei has two pet crows, Phobos and Deimos, that appeared infrequently at the Hikawa Shrine throughout the classic anime. Manga readers realize these were no ordinary birds, though. Named after Mars' real-life moons, these birds were really the Fire Guardian's familiars who could take on human-like forms.
In Dream, Phobos and Deimos play a key role in Sailor Mars' new powers. Later on in the manga, it's revealed the duo is from Coronis, a planet also inhabited by a future Sailor Moon enemy named Sailor Lead Crow.
Luna, Artemis, and Diana will also take on their human forms, if things go according to the manga.
Mamoru is the Golden Crystal's Keeper
After defeating Queen Beryl and the Black Moon Clan in the classic '90s Sailor Moon anime, Mamoru became less integral to the overall story and often stood aside as the Sailor Guardians battled the enemies. The manga shows him being less of a bystander and more proactive in the fight against evil, though.
SuperS confirmed Prince Endymion was indeed Earth's own Guardian, but what it didn't do was state the Golden Crystal was his. The manga shows the Golden Crystal is physically inside Mamoru and is also his Sailor Crystal that Sailor Galaxia seizes in the final manga arc, Stars. Meanwhile, in the original anime, the Golden Crystal belongs to Helios and has no relation to Mamoru or own his Star Seed, which resembles the Golden Crystal.
The Sailor Quartet Will Appear
The '90s anime failed to fully adapt the Amazoness Quartet's story from the manga. By that, the Amazoness are actually Sailor Chibi-Moon's own Sailor Guardians who would go on to protect her in the future. VesVes, PallaPalla, JunJun, and CereCere respectively become Sailor Vesta, Sailor Pallas, Sailor Juno, and Sailor Ceres.
At the end of SuperS, the Amazoness Quartet became good and even hinted at seeing Chibi-Usa and the others again. Of course, this never happened, so the manga's fans are excited to see Eternal giving the Sailor Quartet their rightful on-screen debut.
No Dream or Golden Mirrors
In the 1992 anime, the enemies often went in search of "MacGuffins" like Rainbow Crystals, Talismans, Star Seeds, and, of course, the Golden Mirror in SuperS. This object or Dream Mirrors in general did not appear in the manga, though.
Dream Mirrors were yet another magical item akin to souls that resided in people's bodies, and the one person who hid Pegasus in their dreams would host a special Dream Mirror that was golden in color. Eternal will undoubtedly not feature these objects or too many Lemures, the spirit-like monsters employed by the Dead Moon Circus.
New Powers for the Inner Guardians
While the '90s anime skipped the "Planet Power" upgrades for Sailor Mercury, Sailor Mars, Sailor Jupiter, and Sailor Venus, SuperS did give the four Inner Guardians their respective power-ups. Be that as it may, their new transformations and attacks in that version were the result of Pegasus' magic.
In the manga, Mercury, Mars, Jupiter, and Venus receive new powers after acquiring their Sailor Crystals through unique means.
Double Moon Gorgeous Meditation
In SuperS, Super Sailor Chibi-Moon didn't have any actual offensive powers beyond firing a weak energy beam à la "Pink Sugar Heart Attack" from her Crystal Carillon during a filler episode. For the most part, all Chibi-Moon did was summon Pegasus so Super Sailor Moon could then finish the Lemures off with "Moon Gorgeous Meditation."
Yet in the manga, Chibi-Moon has a more active role when it came to the battles. She didn't use the Crystal Carillon, which was much smaller, in conjunction with "Twinkle Yell" more than once, and she had her own Kaleidomoon Scope like in the SuperS movie. She and Sailor Moon can perform "Moon Gorgeous Meditation" together or individually.
Queen Nehalennia's Origin Will Be Different
In SuperS, the ruler of the Dead Moon Circus, Queen Nehalennia, was once a victim of her pathological and dangerous desire to stay young and beautiful. In her own asteroid kingdom, the young woman gave in to a "voice" inside of her head that caused her to kill her royal followers; they all became Lemures after she devoured their dreams. In return, Queen Nehalennia became eternally youthful in spite of her crimes. Eventually, Sailor Moon forgave her and sent her back in time to relive her childhood without the fate of becoming evil.
In the manga, Queen Nehalennia was a dark force who practically haunted Queen Serenity in the Silver Millennium. She lived at the center of the Moon, and when she made her appearance at a party celebrating Princess Serenity's birth, Queen Serenity sentenced Queen Nehalennia to live out her life inside a mirror. This was before Nehalennia cursed the Silver Millennium, which later came true when the Dark Kingdom destroyed it.