Cover Page: Enel's Great Space Operations, Vol. 31: "Within the Darkness, An Underground City".

The tunnel leads Enel to an unbelievable sight: a vast and ancient city, which has lain below the moon's surface for untold generations.

Usopp has finally seen through Perona's tricks, and uses a fake hammer that weighs 10 tons to beat Perona. Zoro challenges the samurai Ryuma, and their battle begins in earnest.

Having finally pierced the veil on Perona's tactics, Usopp takes time to review the facts: Perona is visible to the naked eye, but is capable of phasing through people and objects effortlessly. She can also fly, and change her size at will, so a person who didn't know any better would assume that she isn't made of flesh and blood. However, based on how she ran from him as he chased her, it was clear in that particular instance that she did indeed have a physical body. He thus concludes that the Perona he has been fighting is merely a ghost that was created when he initially lost sight of her. Usopp calls attention to Perona's real body sitting motionless on a bed in the chamber in front of them, and asserts that he will no longer be fooled. Perona praises Usopp for being much more intelligent than she assumed, and notes how the Sogeking mask seems to have given him confidence. She clarifies however, that rather than a "ghost" that is being controlled by her real body, the form Usopp sees in front of him is her actual spirit. She is capable of separating this spirit from her physical body at will. Usopp questions what would happen if she has no physical body to go back to, as he fires "Daibakuhatsu Boshi" at it. Perona screams out in protest, but is relieved when the projectile appears to miss. Usopp states he needs to fire another shot, but Perona doesn't give him the chance, sending a "Toku Hollow" at him. Usopp surmises that this is a larger version of her "Mini Hollows", so allowing it to detonate would instantly kill him. The ghost bites down on his upper body, and Perona uses the opportunity to return to her physical body. As she re-awakens, she confirms that she can detonate this hollow as well by snapping her fingers, using "Kamikaze Rap". To her surprise, the ghost completely vanishes, and it is revealed that Usopp absorbed the blast using an Impact Dial. Before she can follow up with another attack, Perona realizes that her arm has been stuck to the bed. Usopp divulges that the attack he fired at her earlier was actually "Torimochi Boshi", and that he didn't miss, as his plan all along was to immobilize her once she returned to her physical body. This way, he could deal with both her physical and spiritual presences at the same time. As Usopp prepares to finish her off, a Wild Zombie, The Gallant Hippo, emerges and accosts Usopp for his defeat of Kumashi. Usopp however releases the absorbed impact from the Toku Hollow, instantly defeating the Hippo. Perona is in awe of the strength Usopp displays, though Usopp himself mentally notes the pain from the recoil of the impact dial. He fires "Kurobikashi Boshi" at the Ghost Princess, which results in cockroaches appearing all over her body. This is revealed to have been a ploy as well, as the attack is actually "Gokiburi Boshi". Perona screams in horror loud enough to be heard outside the mansion, as she frantically tries to get the roaches off of her and begs for Kumashi to come save her. Usopp says that she may be afraid of roaches, but she has a lot more to fear from him, as she truly underestimated him. As he pulls out the 10-Ton Usopp Hammer, he states that no one in the East Blue is feared more for their superhuman strength. Believing the hammer is truly 10 tons, a grief-stricken Perona asks where Usopp got this kind of strength from, and pleads for him not to hurt her. She continues to desperately beg to be forgiven and promises not to harm the Straw Hats, but this falls on deaf ears as he smashes the hammer down on her head with "Usopp Golden Pound". The "hammer" is revealed to be a balloon that pops instantly upon impact, but the psychological trauma of the attack causes Perona to pass out and foam at the mouth. Usopp expresses shock that the "Ghost Princess" of a haunted mansion wouldn't be able to tell a real hammer from a balloon, or plastic cockroaches from real ones, but nevertheless asserts that she had no idea who she was messing with when she tried to use negativity and lies as her weapons.

Elsewhere in Thriller Bark, Zoro is seen falling from the tower of Dr. Hogback's mansion as a flaming figure stands atop of it. Zoro crashes into one of the tower windows, and this figure is revealed to be Ryuma. Franky notes that the samurai appears to have said something, and Brook wonders what it means exactly. Brook however also notes that the fight is over, as he comments that he's never seen a fight like this. As Zoro lay motionless, Brook realizes that Ryuma never actually took him seriously in any of their fights.

In a flashback, it is shown that just five minutes earlier, Zoro and Ryuma had begun to face off with one another in Hogback's laboratory. Zoro has announced his intentions to take Shusui from the samurai, who comments on Zoro's abrasive nature. Ryuma inquires as to why Zoro wants his when he already carries three swords, and the latter clarifies that one of them is broken. Zoro however doesn't feel right not carrying it at all, as he is a Three Sword Style user. Ryuma has never heard of a 'Three-Sword Style' before, and wonders if it is some kind of circus act. Zoro laments that he won't be able to show the samurai, but nevertheless affirms that he will be breaking what's left of his nose. Ryuma shares in this disappointment, and notes that Zoro seems fairly powerful. In fact, he likens the anticipation of his fight with Zoro to when he fought a towering monstrous creature, but he can't seem to fully recall. Zoro charges Ryuma in an instant, and the impact of their blades clashing astonishes Franky and Brook. The force of the clash also rattles the tiles of the floor beneath them, as the two warriors exchange steel once more. Ryuma uses "Aubade Coup Droit", which Zoro is able to dodge at the last second. Although the attack is a thrust, it is shown to be powerful enough to weaponize the air itself and pierce a hole through the brick wall behind Zoro. Franky asks if Ryuma just fired a gun, and Brook notes that the technique has never been that powerful when he's used it. Zoro smiles, pleased with the strength of his opponent.

Chapter Notes:
Usopp defeats Perona.
The Gallant Hippo, one of Perona's Wild Zombies, appears and is defeated by Usopp. 
Perona reveals a larger version of her "Mini Hollows", the Toku Hollow. The increase in size also reflects an increase in power.
Usopp reveals a new version of the Usopp Hammer, which weighs "10 tons" - 5 more "tons" than its predecessor.
The Gallant Hippo, one of Perona's Wild Zombies, appears and is defeated by Usopp.
Perona reveals a larger version of her "Mini Hollows", the Toku Hollow. The increase in size also reflects an increase in power.
Usopp reveals a new version of the Usopp Hammer, which weighs "10 tons" - 5 more "tons" than its predecessor.
The conclusion of Zoro and Ryuma's fight is shown, but the winner is left ambiguous.
Zoro begins fighting Ryuma, though the entire fight is revealed to be a flashback that occurred 5 minutes prior to Usopp's victory.
Ryuma is still using Brook's techniques, however with greatly increased power.
Brook realizes that Ryuma was never actually taking him seriously, though this is likely related to how Brook's death would be problematic for the zombie.
Fighting Zoro gives Ryuma a feeling of facing a monstrous creature, hinting that there are still remnants of the samurai's original memories despite how much time has passed.
Ryuma is still using Brook's techniques, however with greatly increased power.
Brook realizes that Ryuma was never actually taking him seriously, though this is likely related to how Brook's death would be problematic for the zombie.
Brook realizes that Ryuma was never actually taking him seriously, though this is likely related to how Brook's death would be problematic for the zombie.
Fighting Zoro gives Ryuma a feeling of facing a monstrous creature, hinting that there are still remnants of the samurai's original memories despite how much time has passed.