Key Takeaways
- Merfolk are genetic relatives of fish-men, with both facing historical oppression and slavery.
- Strong merfolk, like Hyouzou and Aladine, can hold their own in combat.
- Shirahoshi, is likely the most powerful mermaid, due to being an ancient weapon.
Merfolk are a somewhat niche, but active species in One Piece. They are genetic relatives of fish-men, with the main difference being that fish-men’s fishlike characteristics are more prevalent on top rather than below. Like fish-men, merfolk are also biologically compatible with humans, as the three races have a deeper ancestral connection.
Nonetheless, historical oppressive attitudes, as well as merfolk being highly-valued slaves, mean a majority of them are forced to stay underwater. Even so, it has been shown that some merfolk are perfectly capable of fighting for themselves. Here are some of the strongest merfolk shown in One Piece thus far.
5 Hyouzou
Officer/Hired Sword Of The New Fish-Man Pirates
- Debut: Chapter 607 (Manga), Episode 527 (Anime)
- Species: Blue-Ringed Octopus Merman
Hyouzou was once considered the strongest swordsman on fish-man island. He was notably scouted by Arlong, but the pair’s partnership failed to solidify because Arlong was unwilling to pay for his services. Hyouzou claims it is for this reason that Hatchan, an octopus fish-man also skilled with the sword, was a part of the Arlong Pirates instead.
Hody Jones learned from Arlong’s mistake and was willing to pay Hyouzou. The merman was ambivalent towards Hody’s ideals, but acted as an officer because he was paid to do so. He is shown to be fast enough to block Luffy in his Gear 2 form, and can take out many foes. Due to taking after a blue-ringed octopus, he is also capable of secreting toxins. Hyouzou was ultimately no match for Zoro, a fact that was compounded after excessive energy steroid consumption rapidly aged him into a feeble old merman.
4 Aladine
First Mate/Doctor Of The Sun Pirates
- Debut: Chapter 620 (Manga), Episode 540 (Anime)
- Species: Goatsbeard Brotula Merman
Aladine was once a slave alongside his former captain, Fisher Tiger, and many of his crewmates. He is currently the only named member of the Sun Pirates to have both been with the crew prior to Tiger’s death and to remain with them to the present day, as most of his known crewmates formed or joined other pirate crews after the fact. When Jimbei was captain, he became the second-in-command, and it is quite possible he may now be captain due to Jimbei’s own departure.
In addition to his medical training, Aladine is skilled in fish-man karate, capable of clashing against the likes of Charlotte Oven, a noted officer of the Big Mom Pirates. Like most of his kind, he is also a capable swimmer, although unlike some mermen, his body type allows him to be on land without additional help.
3 The Neptune Brothers
Princes Of Ryugu Kingdom
- Debut: Chapter 609 (Manga), Episode 528 (Anime)
- Species: Shark Merman (Fukaboshi), Oarfish Merman (Ryuboshi), and Opah Merman (Manboshi)
Fukaboshi is one of Neptune and Otohime’s three sons, and is next in line for the throne. Like his family, he is sincerely dedicated to his mother’s dream of peaceful relations with humans, even in the face of adversity from humans or fish-men. He is shown to be serious and dutiful in general, in contrast to his younger brothers, Ryuboshi and Manboshi, who are a more comical duo.
All three of them are quite strong, with the New Fish-Man Pirates needing to take energy steroids in order to supercede their abilities. Unlike their father, the three are still in their relative prime, with Fukaboshi in particular showing the ability to recover from his injuries fairly fast. That said, they were no match for the pirates once they consumed the steroids, relying on the Straw Hats and Jimbei to help aid them further.
2 Neptune
Ruler Of Ryugu Kingdom
- Debut: Chapter 611 (Manga), Episode 530 (Anime)
- Species: Coelacanth Merman
Neptune is the husband of the late Otohime, a beloved mermaid ruler who wished for peace. Neptune worked tirelessly to keep his late wife’s dream alive, and is generally well-liked by his subjects. He is also capable of communicating with whales, a relatively rare skill for mermen. He primarily uses this to communicate with his gigantic pet whale, Hoe, who also serves as a means of transportation.
Even into his 70s, Neptune is a mighty merman, capable of withstanding attacks from Hody even after the pirate’s energy steroid consumption. That said, his age has caught up with him, to the point where even his physical endurance can be outmatched by him overexerting himself in combat.
1 Shirahoshi
Princess Of Ryugu Kingdom
- Debut: Chapter 612 (Manga), Episode 531 (Anime)
- Species: Smelt-Whiting Mermaid
Shirahoshi is the sole daughter of Neptune and Otohime. She is noted for her gigantic size, being larger than her mother and elder brothers at less than one year of age. She is quite fragile, having spent most of her life inside a locked tower and being pampered by her family. Her fragility is such that Luffy notably called her a crybaby when the two became acquainted. She needed him to guard her upon leaving her quarters for the first time in several years.
While she attempts to be braver upon joining her family for the Levely, she is quickly captured by the World Noble Charlos, who wishes to make her a slave. Nonetheless, thanks to some timely intervention from fellow World Noble Donquixote Mjosgard, along with Sai and Leo of the Straw Hat Grand Fleet, the young mermaid was saved.
Despite her vulnerable state at present, it is a real possibility that Shirahoshi is far more powerful than her relatives have put together. This is due to her being the ancient weapon, Poseidon, a trait she inherited from a distant ancestor. Poseidon’s main asset is the ability to control and communicate with sea kings, powerful beings that populate every known ocean. They respond to her feelings and desires, such as her wish that Luffy would be helped, even if she did not directly request their assistance. Beyond this fact, she could likely grow in physical strength if she wished to, seeing as her relatives are among the most powerful merfolk in existence.