One Piece might be a series about pirates, but there is no shortage of scientific marvels in it. Oda has not shied away from incorporating scientific elements into his story. Some people might think that it does not gel, but the reality is that it blends in nicely with the rest of the story.
There are plenty of smart characters in One Piece, and they have created some outstanding pieces of technology. Dr. Vegapunk alone has been responsible for the creation of several incredible technologies. While most inventors try to make something that would be useful for the common populace, there are others who have made dangerous technological weapons as well.
8 Reject Dial
​​​​​Dials were introduced in the Skypiea arc. They are made from the remains of shellfish that are found in the sea in Skypiea. Dials are capable of storing matter as well as energy, which makes them very useful. There are various kinds of Dials, and each of them serves a specific purpose. Some of the Dials are also useful for combative purposes.
Reject Dial is one of the strongest Dials in the series. It is a stronger version of Impact Dial that releases the stored impact all at once and increases its power by a significant margin. However, the Reject Dial also harms the user's body. It can cause everlasting damage, so most people tend to avoid it.
7 Sea Beast Weapons
The Sea Beast Weapons are one of Vegapunk's many creations. The scientist made several modifications to any Sea Beasts that he could find. These enhancements made them more dangerous than normal Sea Beasts.
The Sea Beast Weapons were tasked with the responsibility of keeping out intruders. Even Rob Lucci was wary of the threat that they posed to CP0 and their ship. So he decided to take the easy way out by using S-Bear's power to infiltrate Vegapunk's laboratory.
6 Raid Suits
Since their introduction, Raid Suits have cemented their status as one of the coolest inventions in the series. They have been created by Judge for his family. They have been used by the Vinsmoke family to obliterate their enemies. Raid Suits are kept in a canister when not in use, making them easy to carry. Once a person uses their Raid Suit, they become more durable and agile.
The shoes are fitted with special flotation devices and an accelerator. These increase the power of their kicks and allow them to cover large distances. The cape of the Raid Suits is bulletproof, and it can withstand a barrage of gunfire.
5 Laser Weapons
Kizaru's Pika Pika no Mi is one of the most lethal Devil Fruits in the entire series. The Navy Admiral ate it at some point in his life and gained surreal powers. The Pika Pika no Mi has a lot of potential for destruction, which is why Dr. Vegapunk spent years studying it.
Vegapunk's efforts paid off as he was able to incorporate the lasers created by the Pika Pika no Mi into his other creations, such as the Pacifista and the Seraphim. These lasers can cause widespread damage, as seen in many instances throughout the series. Vegapunk also used the lasers for his defense system on Egghead Island.
4 Plague Rounds
It is not recommended to fight the enemy, especially in situations where the enemy has a numerical advantage. To circumvent this problem, certain characters came up with lethal biological weapons to subdue their enemies. However, launching these weapons is not easy, so Queen came up with Plague Rounds. These bullets contain the viruses created by Queen.
Queen used Plague Rounds to launch the Ice Oni virus to increase the casualties on Onigashima. The virus spreads quickly from one person to another, and it is almost impossible to control its spread without antibodies. An infected person slowly starts to turn into an ice oni and begins to lose their mind. They eventually die from excessive physical exertion.
3 Bubble Gun
Bubble Gun is the last name a person would think of when naming a dangerous piece of technology. However, it is arguably one of Vegapunk's best inventions. Lilith, one of Vegapunk's satellites, was seen using Bubble Gun in her fight with S-Snake.
Bubble Gun shoots bubbles that are made of sea energy, making them the bane of Devil Fruit users. S-Snake had her energy drained despite only being grazed ever so slightly by one of the bubbles. If this weapon were to fall into the hands of the wrong person, they could easily defeat the strongest Devil Fruit users.
2 Pacifista
The Pacifista have been created by Dr. Vegapunk. These cyborgs are made to serve the Marines. The original Pacifista were modeled after Bartholomew Kuma, but they were later modified and given different designs. The advanced versions of the Pacifista are called the Seraphim.
According to Dr. Vegapunk, the Seraphim are the strongest form of humanity. These weapons of mass destruction are designed after the younger versions of the former Shichibukai. The Seraphim also possess Lunarian traits, which boost their overall strength. Both the Pacifista and the Seraphim possess immense durability. They can effortlessly fight and defeat some of the most powerful characters in the series.
1 Iron Giant
The Iron Giant was created during the Void Century. It was very likely made by the people of the Ancient Kingdom. The Iron Giant is a massive robot that is just as big as the ancient giants. Two hundred years prior to the start of the story, the Iron Giant appeared out of nowhere and attacked Marijoa.
Luckily for the Celestial Dragons, the robot ran out of energy and couldn't cause any major damage. Considering the size of the Iron Giant, it is safe to assume that it could decimate an entire city with ease.