Koby

In his first appearance, Koby was a small, timid, chubby boy with kobi pink hair and round-frame glasses.[1]

Due to the passage of time and Garp's training, Koby has grown thinner and taller, standing close to Luffy in height. He has also gained a cross-shaped scar above his right eye, presumably earned under Garp's heavy-handed tutelage. His hair has grown longer and shaggier since his growth spurt, but it has retained its kobi pink color.

Koby wears a standard-issue Marine jacket, pants, and neckerchief as well as a brightly patterned bandanna worn tied across his forehead. Koby's glasses are still present, but he has adopted the habit of wearing them pushed up on his forehead, occasionally using them for reading.

After the timeskip, Koby has grown even taller, reaching Garp's shoulders. He now wears a scarf, a senior officer's Marine coat with the word "justice" on it, a merit on his jacket, and a new bandanna. The scar on his forehead also has grown wider.

Koby was first introduced as the Alvida Pirates' hapless ship caretaker who lived in fear of both the ship's crew and captain. Two years of forced servitude had robbed him of all hope of escaping as well as his dream of becoming a Marine, leaving him with few goals other than avoiding being bludgeoned to death by Alvida's iron mace. Luffy was less than impressed with Koby's cowardice, describing him as "pretty stupid and useless...and kinda wimpy too". However, Luffy's boundless optimism and single-minded pursuit of his dream rekindled a similar conviction in the downtrodden ship caretaker, allowing him to defy his captors, even under the threat of a brutal death by Alvida's mace.[1]

As the pair continued in their travels, Koby remained timid and cautious, often relying on Luffy to perform dangerous tasks and becoming alarmed by his companion's reckless behavior.

He was also shown to be perceptive, noting that it was "strange" for the citizens of Shells Town to be afraid of a Marine Captain and telling Luffy that he had "a bad feeling about this." Koby's naïve belief in the blanket integrity of the Marines was dashed when he witnessed the actions of Axe-Hand Morgan and his son, but it only strengthened his resolve to become, in his words, "a real Marine."[16]

Under Garp's instruction, Koby's timidity has been replaced with confidence, although he remains polite, self-effacing, and apologetic if he feels he has done something overly ambitious (such as publicly stating his goal to become a Marine admiral). He continues to be an emotional, compassionate person who can easily be driven to tears for a variety of reasons, which led to Zoro jocularly calling him a "crybaby" during their reunion at Water 7.

In his first appearance, Koby lacked any fighting skills, let alone even above-average physical prowess. According to Alvida, the only reason she kept him around was because he happened to be good at navigation.[1] He gained some fighting skills after he trained under Vice Admiral Monkey D. Garp, alongside Helmeppo, learning the Rokushiki, surprising Luffy and Zoro from the amount of growth he'd undergone. After the two-year timeskip, Koby reached the rank of Captain, granting him command over lower-ranked Marines and charge of his own ship. In addition to this, at some point he became a member of the covert Marine squadron SWORD, who are granted enough free reign to take on missions normal Marines could not, including challenging any of the Four Emperors.

At some point, he became regarded as a "Hero" because of the Rocky Port Incident, somehow assisting the Emperor, Blackbeard in defeating Ochoku, a former member of the Rocks Pirates and a famous pirate comparable to Shiki and Captain John.[13] During the Marines' invasion of Amazon Lily to arrest the former Warlord, Boa Hancock, Koby was one of the few people to not get petrified by her powers: a notable feat as Yamakaji, Catarina Devon, Vasco Shot, a Vice Admiral and two of the Blackbeard Pirates' Titanic Captains were among the Marines and pirates to be petrified. After the Cross Guild placed bounties on Marines, his was Beli 500,000,000, most notable as most Marine Captains are worth Beli 100,000,000.

He has some knowledge of swordsmanship, as he was seen practicing with Helmeppo and Bogard.