Dragon Ball Z has a reputation as the greatest action anime ever, earned through its insane combat, in which god-like heroes and villains fight atop crumbling planets. Because so many characters are so absurdly powerful, it's sometimes mistakenly believed they are, somehow, unmatched in any fiction. However, if you look at the limits of Goku's abilities, there are several other anime characters with more power.
For instance, there's the Super Tengen Toppa Gurren Lagann, a universe-sized robot that throws galaxies like shuriken; Saitama, who defeats every adversary in one punch; and even Haruhi Suzumiya, a god who can rewrite reality on a whim. But one character you might never expect to be stronger than Goku is Usagi Tsukino, better known as Sailor Moon. Let's go to the tale of the tape.
Goku Outclasses Usagi in Physical Strength
Sailor Moon is not really thought of as a "fighting series"; it features very few all-out brawls. Usagi isn't particularly that strong physically, and she has no martial-arts training. If Goku were to get into a fist fight with Usagi, he would undoubtedly knock her down, hard.
However, Usagi is surprisingly durable. Except for that time she fought an entire battle on a spaceship that amplified the gravity to more than 10 times that of Earth. In Sailor Moon R, Usagi combats Rubeus, a member of the Black Moon Clan, who uses his ship's gravity-alteration device to toss her around, transitioning from zero gravity to "super gravity." Yet, despite enduring gravity fluctuation comparable to that under which Goku trained en route to Namek, Usagi rises to her feet.
The fight takes place less than a year after Usagi became Sailor Moon. It took Goku decades to do what Usagi can accomplish naturally.
Usagi also often takes a brutal amount of punishment, but no instance comes close to the time she dived into the Galaxy Cauldron, force of raw universal that can create and destroy all things. And she survived! Sure, Goku can trade blows with the God of Destruction Beerus, but Usagi survived cosmic destructive forces.
Usagi, Destroyer of Worlds
Usagi is a normal human being; Mr. Satan is stronger than her. However, when transformed into Sailor Moon, she has the ability to destroy planets.
Wiseman, the primary antagonist of the Sailor Moon manga's second arc, is a sentient planet -- think Marvel's Ego the Living Planet, only with the ability to rip holes through time and space, and eradicate entire worlds with his aura. Well, Usagi and her daughter, Chibiusa, blew up the whole planet.
And that was before Usagi gained the ability to become Super Sailor Moon, or her stronger form, Eternal Sailor Moon. Those transformations multiply her magical abilities, allowing her to combat such threats as Pharaoh 90, an outer-dimensional entity of an almost-Lovecraftian nature.
In the final arc, Eternal Sailor Moon combats Sailor Galaxia, the strongest of all Sailor Soldiers, who possessed the Sapphire Crystal, a counter to Usagi's own Silver Crystal that is powerful enough to ravage galaxies. The final battle of Sailor Moon is fought over whether Galaxia will end all life in the universe -- and Galaxia, quite frankly, gets way closer to accomplishing that than any villain in Dragon Ball Z.
Usagi's Fighting Style Counters Goku's
While Goku's primary fighting style involves martial arts, Usagi rarely engages in physical combat. She instead employs magical attacks from a distance.
All of Usagi's adversaries are powerful on a downright cosmic level. Because most are incorporeal, they're foes that someone like Goku might have a more difficult time facing. Usagi's fighting style, however, is perfectly suited for those kinds of threats, opting for long-range, magical attacks over close-quarters combat.
And we mean long range. The second arcs of both the anime and the manga introduce Usagi's future self, Neo-Queen Serenity, who's able to combat the planet-sized Wiseman from across the solar system, all while living her life and governing Crystal Tokyo.
However, the true source of Usagi's power is love and healing, which can rewrite reality, and even reverse the forces of universal destruction in order to save those she loves. Goku is strong, but there is little he can do that Sailor Moon can't then undo.
But there is one more element that tips the scales decidedly in Sailor Moon's favor: her final form.
Sailor Moon's final incarnation is Sailor Cosmos, essentially, a physical god. She can bend the laws of reality, warping through space and time without difficulty. Even the stars themselves are subject to her power.
The final arc of Sailor Moon reintroduces Chaos, the manifestation of evil and destruction in the universe. Imagine if you combined Kid Buu with Beerus, only given an incorporeal form. Chaos is immortal, cannot be wounded, cannot be hurt, and exists so long as the universe does. You would have to destroy the universe itself in order to destroy Chaos.
In Dragon Ball Super, Goku never truly beats Beerus. He competes, albeit briefly, against him, but doesn't win. By comparison, Sailor Cosmos fights Chaos to a standstill after centuries of non-stop combat. Cosmos becomes the universal force of light and good to counterbalance evil.
So How Can Usagi Beat Goku?
In short, Usagi is capable of feats comparable to Goku. She can survive planet-destroying strikes and, while not as physically strong as Goku, she usually places enough distance between her adversaries and herself to eliminate the need for hand-to-hand combat.
Usagi can beat Goku so long as the fight ends up playing to her strengths. Should Goku move in close, the confrontation could get dicey. However, it's possible Usagi's own abilities, especially as either Eternal Sailor Moon, could keep her on her feet. Should Goku go Super Saiyan Blue or Ultra Instinct, it's possible he could turn the tide against Usagi, especially if in close quarters.
However, given how much punishment Usagi can endure and dish out, it's possible she can outlast Goku. If Usagi can fight Goku using primarily her magic against his ki, she might be able, at her full power, to outlast Goku. But against Sailor Cosmos? Goku might as well fight Zeno.
In many ways, pitting Goku and Sailor Moon against each other is like pitting Superman and Doctor Fate against one another. They're both incredibly powerful. Superman is stronger. But Doctor Fate would probably win because he's basically all-powerful.
Come the end of Sailor Moon, Usagi Tsukino is all-powerful.