WARNING: The following contains spoilers for Sailor Moon Eternal: The Movie, now available on Netflix.
Sailor Moon Eternal has a lot to say about hopes and dreams, as well as fears and dark feelings. Throughout the two-part film, each of the Sailor Guardians gets exposed to both, learning something important about themselves in the process.
For Ami Mizuno (Sailor Mercury), her dream is to become a doctor but fears being unloved by others. Rei Hino (Sailor Mars) wants to succeed her grandfather as the head priestess of the Hikawa shrine but feels a deep resentment towards her father for abandoning her. Makoto Kino (Sailor Jupiter) wishes to marry and become a business owner and doubts being a Sailor Guardian is the right path for her. Minako Aino (Sailor Venus) wants to be an idol but feels like a failure as the Sailor Guardians' leader.
While the first half of Sailor Moon Eternal focuses on the dreams and fears of Usagi Tsukino's closest friends, the second half fleshes out those of Usagi herself, especially as Sailor Moon. What she wishes for vs what she fears is at the heart of her fight with Queen Nehelenia of the Dead Moon Circus, who is the living embodiment of darkness itself. In many ways, the entire Sailor Moon narrative has been building up to this iconic fight that results in Sailor Moon achieving her Eternal form.
In fact, her entire journey has been about defining her own worth and being in charge of her own destiny. When we first met Usagi in Sailor Moon Crystal, she identified as a slacker who loved to eat snacks, take long naps and hated doing homework. As a 14-year-old girl with no life aspirations and who performed poorly in school, she was constantly reminded of her failures by her mother and especially her younger brother Shingo who has little respect for her.
Before her awakening as a Sailor Guardian, Usagi's life was defined by others' opinions of her with no one in her family validating her hopes and dreams. By becoming a Guardian, Usagi not only came to realize the larger place she occupies in the world -- by learning she is the reincarnation of Princess Serenity of the Silver Millennium -- but understands her own values. During her first outings as Sailor Moon, Usagi learned that friendship and family are most important to her. She also believes in protecting the lives and dreams of everyone else in the world, effectively proving why she is the most important Sailor Guardian and the owner of the powerful Legendary Silver Crystal.
Every threat Usagi has faced as Sailor Moon -- from the Dark Kingdom to the Black Moon Clan to the Death Busters -- has been about challenging those values, with Usagi always coming out stronger and more powerful than before. In Sailor Moon Eternal, Queen Nehelenia seeks to do the same to Usagi but on a more personal level. Like Queen Beryl before her, Queen Nehelenia has a history with Usagi in her past life -- especially her mother, the former Queen Serenity of the White Moon Kingdom. In her previous life, Nehelenia resided on the dark side of the moon but was rejected by the former Queen.
Despite Nehelenia reasonably arguing that light cannot exist without dark, Queen Serenity refuted the idea that both should co-exist in harmony. At her infant daughter's christening, the Queen banished Nehelenia to another dimension contained inside a mirror, effectively imprisoning her for millennia. She later explained to a young Princess Serenity, "light and darkness go hand in hand. If you show any tears or fears against the darkness, it will grow big, attack you, and devour all your light. Serenity, to overcome the power of darkness, you must always let your star shine in your heart."
Applied to the fight with Nehelenia, Sailor Moon is more than aware of her insecurities. While Usagi has come a long way since her earlier days as a Sailor Guardian, she still fears rejection by the people she loves, especially Mamoru Chiba, her beloved. In Sailor Moon Eternal, this is the weakness Nehelenia tries to exploit to destroy Usagi and claim the keys to her kingdom. What she doesn't count on is the strong support system Usagi developed with all eight Sailor Guardians, who embody the light she needs to overcome her own darkness.
Usagi being able to remind herself of the mutual love she shares with the most important people in her life is why darkness is never able to consume her light. This realization ultimately allows her to achieve her Eternal form and defeat Nehelenia once and for all by the film's end.
Similarly, Chibi Usa comes to understand her own worth as a Sailor Guardian and her place in her parents' legacy. Realizing what motivates her mother to fight as Sailor Moon also informs the kind of relationship Chibi Usa wants to have with her own Sailor Guardians, the Amazoness Quartet. Her mother's love for her father also informs the kind of relationship she wants to have with the priest of Elysion, Helios, whom she is fated to meet again.