Overview

Being a member of the Kid Pirates, it can be assumed Rails has a decent amount of strength and expertise.

While the extent of her abilities has yet to be fully seen, when fighting against the Marines on Sabaody, she is shown to be well versed in close combat issuing strong kicks and punches. While much smaller and less built than the rest of her crew, Rails makes up for it with her sheer fighting prowess, clearly able to handle her own against an adversary. Despite this, it can be assumed she may not be as battle-prone as her captain, thus she doesn't fight as often.

Rails is primarily seen attacking with her fists or legs, using her Devil Fruit powers to put even more impact on her blows. While this is shown, there is no known move-set she uses like most Devil Fruit users.

She is known to work with weapons along with Kid, so it can be assumed she at least knows how to use most kinds. It is said she has a habit of throwing tools at anyone who interrupts her alone time working, so it can also be assumed she is able to proficiently use items as projectiles.

Since she is a Devil Fruit user, Rails has lost the ability to swim and becomes immobile.

Unlike her crewmates, Rails has a good sense of when to quit. If she feels she cannot benefit from a situation, she takes the initiative to flee or escape. This is seen when Kid challenges Kaido during their first encounter. While not exactly fleeing as her loyalty kept her at her captain's side, Rails knew - similar to Basil Hawkins - that this was a losing fight. 

Rails is also seen with a keen ability to take machines and mechanisms apart with her brain, able to clearly see the parts instead of the whole. Her extensive knowledge of maintenance and building has allowed her to fully grasp the tools and parts needed to build almost anything. This helps in her ability to take things apart and rebuild, especially when her goal is to rebuild a more efficient model. This is only really seen when Rails first introduces herself to the Strawhats, where she offers advice to Usopp to use a Torx screwdriver over a Slotted one to increase efficiency. She later admits she has a harder time taking things apart with Torx screws, thus increasing the item's ability to withstand possible tampering.

Her physique and mental state don't change much during the timeskip, but it is assumed she has a better grasp of her fighting capabilities. Like the rest of the crew, she possesses a strong will, being resistant to Rayleigh's Haoshoku Haki.

Physical abilities

"Mach Step"

Rails masters Geppo, one of the Rokushiki over the two-year timeskip, understanding that she is completely vulnerable when not on a surface or foundation. Using this, Rails is able to jump on the air itself. This, coupled with her abilities, allows her to move with her Geppo at incredible speeds, only able to be disrupted (like most Geppo users) when her lower half is restrained. She originally learns of this concept through her research of CP9. Her basic research of the Rokushiki allowed for her to perfect her own stylized Geppo, similar to Sanji's "Sky Walk", that she calls "Mach Step".

While arrogant and confident in her own abilities, Rails is not one to disregard observing others in order to better hone her craft. In her case, Rails would most likely say that she "took Geppo apart and rebuilt it into something more efficient for herself".

construction and engineering expertise

Most of Rails's talent and abilities are rather unknown, as she is not from Water 7 or a headline member of the Kid Pirates. The only real way her abilities are known is through Franky, who mentions her abilities as a first-rate craftsman and considers her a potential rival and fellow engineer. Due to their shared interests, it can be assumed Franky knows more about her than the rest of his crew, as he is well aware of her abilities and natural talent before she even officially meets the crew. Franky also comments that if she were an apprentice under Tom like he and Iceberg, Rails would be even more competent and capable than she is now, implying that her lack of notoriety and any flaws in her skills are due to her not having a stable mentor.

Despite this, Rails has a very unique ability that allows her to be able to mentally take apart almost any handmade creation. This could be due to her affinity for taking things apart as a child, but it is not directly explained whether it's a natural ability or something learned. Through this, Rails is able to take into account the parts of the whole - which also allows her to work much more efficiently and effectively without necessarily even having to physically take anything apart. While there is no official name for this ability, it has been dubbed "God Construct" and "Divine Reparate".

devil fruit

Soku Soku no Mi

The Soku Soku no Mi is a Paramecia-Type Devil Fruit that allows  the user to move at incredible speeds. "Soku" means "Speed by gears" in  Japanese. It grants the user the ability to move at incredible speeds, even able to break the laws of gravity by running on ceilings or sides of buildings. The user is also able to project an afterimage, which is usually used as a decoy.

The user's entire body is able to move at a fast speed, even a single limb like a punch or a kick. Weapons can even have enhanced speed when in her possession, but once untouched  (except for being used as a projectile) the item returns to its natural state of motion.

The user cannot pass their speed onto another,  so the only way to travel with another person is by carrying them. The abilities of the fruit also give the user an otherwordly metabolism,  thus resulting in bouts of insurmountable hunger and eating bouts. The user also must have a foundation in order to activate the fruit's powers. This means that when in the air, the user is left vulnerable.

Rails obtained these powers at a young age when her curiosity led her to explore a docked pirate ship. She stole the fruit and ate it, gaining incredible powers of speed and agility. Rails normally uses this speed as a defense, oftentimes considered the perfect defense as it is nearly impossible to catch her.

To the naked eye, it may not look like Rails has moved, so her dodging and moving back into place can appear as if the attack went through her.

Rails is able to accelerate at incredible speeds, making her kicks and punches even more effective. 

While she is notably faster than Sanji and Brook, she is unable to run on seawater like the later due to her weighing more. One of the only abilities to rival the Soku Soku ni Mi is the Pika Pika no Mi, as the fruit gives its owner the element of light. The current holder of this fruit is Admiral Kizaru.

Rails has no known special moves created through the use of her Devil Fruit.

haki

Kenbunshoku Haki

Rails learns Haki during her voyage in Paradise, able to use it by her debut in the Sabaody Archipelago Arc. While she is no master, Rails is able to use her Haki effectively enough and developed her abilities before she and her crew traveled into the New World. Her Kenbunshoku Haki allows her reflexes and evasiveness to improve drastically, making her an even harder target to predict. In turn, her ability to predict attacks has enhanced significantly, making her an even more dangerous foe.

weapons

Trench Knife

Past

 Rails was born in the South Blue, specifically on the island of  Daugherty. Said island is large in size but an outlier to the others.  Daugherty is one of the closest islands in the South Blue to the Grand  Line. People usually stop there in hopes of finding a mechanic or shipwright before braving the further ocean treachery. While it is not as known or promising as Water 7, Daugherty is another option on one of the many paths to the New World.

Born into a  family-run business, Rails was introduced to the art of machinery early on. Though not the son her father wanted, she was shown to be very interested in taking things apart to put back together. She loved toying with her father's toolkits at a young age. Klonoa King was one of the best in the trade on the island, highly praised and recommended to brave the trip to Water 7. He was a kind but morally strict man, constantly keeping a more free-spirited and independent Rails grounded and focused on the business. Although he did not like getting involved in illegalities, King was all for helping pirates coming for his services.

Several years later, Rails's little brother Minx was born. Despite being very intelligent and crafty with her work, Rails was eventually cast aside in favor of her younger brother whom her father hoped would take on the business one day. Although disheartened by her lack of time spent with her father in the workshop, Rails did enjoy exploring on her own. Her knack for getting into trouble and stealing went against her father's tried and true ideals, allowing Rails to make a name for herself among  the inhabited parts of the island. Her thievery got the best of her once  as she found a massive vessel docked on the harbor near another  shipwright facility. Embarking on her curiosity, Rails boarded the ship and took a look around, easily recognizing it as a pirate ship. She had worked on ships and machines before with her father and still liked to  tinker with things when she could, but the size of the ship and the overwhelming possibilities was enough for her to snoop around.

During her escapade, Rails was able to pick the lock to a door, finding treasures and oddities beyond her wildest dreams. Despite this, she was mostly drawn to the bright pink fruit propped in a pile of Berries. She was smitten with it simply because it reminded her of her hair.  Curiosity again getting the better of her, Rails took it home with her and hid it in her room. That night she decided to try it, considering it toxic but pushing the thought away. Once she and her family realized her fault and the consequences, they tried to keep her hidden as to not receive retribution from the pirates of the ship. Her father disowned her, informing her that the time would come where she would truly not be apart of the family. A few years passed and Rails had gotten the hang of her abilities, but despite her multipurpose skills was still not allowed to work with her father. At times her family would have her sleep outside or find her own dinner.

While mostly on her own,  Rails liked going through scraps and pieces and tinkering with her own  projects on a nearby shoreline. She found fruit in the miles of forest covering the rest of the island. Rails eventually began sneaking into  her family's workshop and stealing tools and even half-finished projects to work on and practice with. Once she turned 16, Rails took another  trip to her family's place to find that they packed up everything and  left the island for Paradise. Now officially on her own, Rails made  herself at home in the now empty and abandoned workshop.

Rails  tried to bring in clients so she could work on her craft, but her lack of materials and presence amidst the other mechanics and shipwrights held her back. During the past few years, Rails had been working on a few of her own ship models including a blueprint for a submarine. She  even tended to sleep inside a lot of her works in progress that littered the shop.

At around 19, an explosion made an uproar on the boardwalk, Rails branded her dagger and went to check it out. A fight had broken out between a young man and an older pirate captain who was well recognized around the South Blue. She watched them with interest as they scuffled, causing damages to nearby shops. When the older man was taken down, it became the talk of the town. The young man was named  Eustass Kid and was a rookie pirate. He was accompanied by Killer and another few men with unique appearances.

When she went back into town later on for some supplies (to steal), she accidentally bumped into Kid and his crew. In a fit of frustration, Kid lunged at her, yet was surprised at her Devil Fruit powers. They all introduced each other and Rails was told the pirates were there for some last-minute preparations before taking on the Grand Line. Kid had yet to find a good enough shipwright and had apparently been going around destroying shops of those who hadn't met his standards. Due to her prideful nature, Rails didn't think before she offered her own services. Kid smugly knocked her down a peg, causing Rails to further be fired up and continue to press at her skills. The pirates finally relented (mainly Kid who was excited to destroy her workplace and cause more damage).

During their time on the Grand Line, Rails helps develop Victoria Punk to the design and concept it is currently.

Summit War Saga

sabaody archipelago arc

While Kid and her crew spent their time in a bar, Rails had gone out on her own to explore. Thus she was not shown during Kid's first appearance and his fight with Scratchman Apoo.

Rails eventually meets up with her crew and first appears along with the rest of the Kid Pirates at the Human Auctioning House. They came hoping to bid on a certain slave, but it was not up for auction at that time. She was noticeably surprised when Luffy attacked a World Noble. Later, she and the rest of the Kid Pirates were confronted by a Pacifista.

Marineford Arc

Rails, along with the rest of her crew, stay behind on Sabaody to watch the war at Marineford unfold on a big screen. Later, they all went closer to Marineford in their ship to see the war put to an end by Red-Haired Shanks.

post-war arc

After entering the New World, the Kid Pirates docked on an island where Rails and her crewmates captured a group of pirates trying to escape back to Paradise. While not fully involved, Rails was a witness to her crew's crucifixion of the pirates.

Dressrosa Saga

Dressrosa arc

Sometime before the eventual alliance and celebration between the Kid Pirates, the Hawkins Pirates, and the On Air Pirates, Rails takes a trip out to sea with her newest "Wave Rider" invention. As it moves through the user's own physical pedaling, Rails overestimated her Devil Fruit abilities and ended up far out at sea. Coincidentally, she ended up in a similar area as the Strawhat crew and decided to board the Thousand Sunny to observe. This was her official meeting with the crew. Her primary concern was Brook's ability to run on water and Sanji's cooking.

Once she left and made her way back to her crew, Rails realized the newly formed alliance and her crew members celebrating. Before she could interact, the Yonko Kaido landed on their island after jumping from the sky.

Yonko Saga

wano country arc

After the confrontation with Kaido, the Kid Pirates were captured and separated. During her captivity along with the rest of her crew, Rails witnessed Orochi take Killer away to where he'd eventually eat a SMILE and become Kamazo the Manslayer and Orochi's secret assassin. During this time, Orochi had also approached her and offered to relieve her of this prison life and become an oiran - which she refused.

Prior to the Fire Festival, the crew regrouped and on the day of the Fire Festival, the Kid Pirates joined the Straw Hats and Heart Pirates in the battle against the Beasts Pirates. After attacking one of the Beasts Pirates ships, the crew was shocked to hear that Kaido formed an alliance with Big Mom.

After the Straw Hats took over the port in front of Onigashima, the Kid Pirates promised to be the ones who would defeat Kaido. After disembarking on Onigashima, the Kid Pirates received Beasts Pirates disguises from Kin'emon. As the alliance began their raid, the Kid Pirates went ahead of the Straw Hats. The crew donned Beast Pirate disguises and began their attack.

While Kid and Killer blew through Kaido's forces and made their way to him along with Strawhat Luffy and Trafalgar Law, Rails remained on the lower floors managing the rest of her crew in her captain and First Mate's absence.