Onigashima is a New World island and a region of Wano Country, which serves as the official base of operations for the Beasts Pirates, including Emperor Kaido, the All-Stars, and the Numbers. The island was dubbed Onigashima upon being settled by the Beasts Pirates over 25 years ago.
Onigashima is a mountainous island that is very difficult to access outside the front gate, which connects directly to the sea, allowing ships to sail in. The waters surrounding the island are apparently lined with whirlpools that make navigating around it nearly impossible unless one utilizes specialized watercraft like a submarine. Thunderstorms are very frequent and even blizzards can happen, sometimes independent to the rest of the island.
The island itself has a port where ships can dock. Notable structures in this port include a gigantic katana piercing the ground, water spouters that resemble oni faces, and an enormous wagasa decorated with paper lanterns. The entrance to the port is lined with two statues depicting kitsune and a stairwell appears to connect the port to the interior of the Skull Dome in the center. There is also at least one lookout station for those who are in guard duty.
Onigashima has two roads that can be used to bypass the island from around the Skull Dome: one to the east and another to the south. The eastern path has a large lake lined with wisteria trees where a brothel and boardwalk system are built upon.
Due to Kaido's ability, it is being levitated and heading towards the capital.
The torii is a small fortress located at sea, right in front of Onigashima and with an actual, gigantic torii gate towering over it. It is heavily armed and serves as the first line of defense of the Beasts Pirates, having a number of the crew's soldiers stationed there.
During the Onigashima raid, it was attacked and neutralized by the Straw Hat Pirates.
Denjiro was able to trick Sasaki and tie him up to this tree as the former's forces infiltrated Kaido's home through the southwestern gate. Sasaki was eventually freed by Big Mom's Ikoku, which cut the tree down as the shockwave caused by the attack pierced through a large portion of Onigashima.
Woman Trouble (女難 Jonan?) is a brothel located to the east of Onigashima. It is owned by Black Maria and directly leads to the insides of the Skull Dome, being a newly added expansion not found in the original blueprints of Kaido's castle. It is built atop a lake and decorated with wisteria shrubs from nearby trees as well as horn-resembling roof protrusions. It directly connects to a long boardwalk that spans from one of the lake's shorelines to the other. During the Golden Kagura, Big Mom stayed here in order to try on a kimono.
According to Big Mom, the building leads into the Live Floor, from the east.
- Further information: Skull Dome
|Black Maria||Bao Huang||Jaki||Goki||Nangi|
|Yamato||Eustass Kid ‡|
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- ≠: the character is non-canon.
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Three years ago, Ace arrived at the island to confront Kaido and met Yamato. During the fight, he melted a dragon statue.
X Drake and some other Beasts Pirates were outside Kaido's lair on Onigashima when they received news of Joker's defeat, which they tried shouting out to Kaido, unaware that he had gone to the Ballon Terminal.
Four Emperors Saga
Sometime later, Kaido returned to his lair and received a call from Scratchmen Apoo, telling him they lost contact with Jack. Realizing his plans to take back Doflamingo had failed, Kaido drank a lot and suffered from intense mood swings, including a rage that caused him to hit some of his subordinates through the roof of his lair.
Wano Country Arc
After Queen captured Big Mom and brought her to Onigashima, Kaido and Big Mom met face to face and the two clashed until they decided to form an alliance to conquer the world. Around this time, the Numbers also return alongside Scratchmen Apoo to Onigashima for the Fire Festival.
On the day of the Fire Festival, the Ninja-Pirate-Mink-Samurai Alliance commenced the raid on Onigashima. The Straw Hats reached the torii and defeated all the Beasts Pirates members stationed there. Having revealed to be a spy for Orochi, Kanjuro captured Momonosuke after a brief fight with his former comrades and then flew to Onigashima to meet with Kaido and Orochi. After the rest of the Alliance arrived at Onigashima, they had then split themselves into different smaller groups, approaching different areas and infiltrating Kaido's castle. After different encounters (including the Nine Red Scabbards fighting the traitor, Kurozumi Kanjuro, and Luffy clashing with two of the Tobiroppo, Page One and Ulti, until he was saved by Yamato), the Nine Red Scabbards and Izo then regrouped.
Kaido would later explain the New Onigashima Project, in which he would transform Wano into an pirate nation, find the Ancient Weapons and the One Piece together with the Big Mom Pirates, and have Yamato become the new shogun of Wano. When Orochi objected, Kaido immediately decapitated him, ending their alliance. He then asked Orochi's subordinates to either join his crew or die. Without hesitation, they declared their allegiance to Kaido. As he was about to execute Momonosuke, Kaido was ambushed by the Nine Red Scabbards. After suffering small injuries, Kaido decided to fly to the top of the dome, taking the samurais with him. He was then later joined by Jack, Nangi, and some Beasts Pirates members while they were all facing the gathered Mink Tribe forces, preparing to engage in a fierce battle.
In the dome, the Alliance tried to save Momonosuke from his execution. While Shinobu failed to save him, Sanji was able to release Momonosuke from his chains while scuffling with King. Yamato, who previously severed the relationship with Kaido after discovering he was willing to kill his own child, was then tasked by Luffy to protect Momonosuke. Luffy, however, faced the wrath of Big Mom who wanted revenge on Luffy for ruining the festival, her tea party, and humiliating her in the public. Luffy then declared he wanted to take down Big Mom, Kaido, and Orochi, effectively declaring war on them. Big Mom then aimed an attack on Luffy, destroying a part of the castle with "Ikoku: Elbaf", but before she could attack once more, she was send out of the castle by both Jinbe and Robin. The Straw Hats then battled some Numbers as well as the Beasts Pirates, when they gathered together in the center of the castle. Luffy then stated he wanted to take down Kaido and reach the top of the dome, asking his crew to back him up and ensure he reached the top. Luffy would then take down some Numbers, when he was joined by X Drake, who was previously declared an enemy of the Beasts Pirates by Who's-Who, and asked to join the alliance.
As the war raged on, Kaido used his power to lift the entire island and began moving it to the Flower Capital.
- In early concept sketches of Franky's "Franosuke" appearance, Onigashima was referred to as "Ryugashima" (龍ヶ島 Ryūgashima?) which translates to "dragon island" instead of "oni island".
- The island shares its name with an island in the Japanese folktale of Momotarō, where the titular hero and his animal retainers went to defeat the residing demons that were troubling people, similar to how the Ninja-Pirate-Mink-Samurai Alliance plans to take down Kaido, who was oppressing the people of Wano Country.
- When Onigashima was first depicted in Chapter 793, it appeared to be a foggy island and the silhouetted skull-shaped mountain was significantly taller.