Kaku is first seen as one of the five foremen of Galley-La Company's Dock One and specializes in mechanics, diagnostics, and housecalls. It was Kaku who inspected the Going Merry  and informed the Straw Hats that it was broken beyond repair. Later on, it was revealed that Kaku was a member of CP9, operating undercover in order to obtain the Pluton blueprints from Iceburg. Along with his colleagues, he has been dismissed from CP9 by Spandam.
When he worked for the Galley-La Company, he wore a white cap, a high-collared orange shirt with blue sleeves, jeans and white sneakers.
In SBS volume 44 he was depicted in an SBS as a child, in which shows him to have fluffy hair, a shorter nose (though still long by his age standards), and wore a cap backwards.
Despite his role as a villain, Kaku is surprisingly honest, even to his enemies and even more so than Fukuro, though he does not seem to take insults well. As soon as his hybrid (giraffe/human) form was mocked, he sliced the Tower of Justice in half, in a rage of embarrassment.
He also talks like an old man, as remarked by several characters, despite being only 23 years old. He uses the term "washi" (meaning I, though used mainly by elders), rather than ore (also meaning I, a masculine term used by young adults).
After being revealed as one of the Water 7 CP9 agents, Kaku's personality becomes rather cold and dispassionate in contrast to his character on Water 7, where he was mainly seen laughing and smiling. Despite this, he often taunts his opponents during battle, ate a Devil Fruit for the fun of it, and exclaimed "This is fun!" during his life-and-death battle with Zoro. He also seems to place a chance to fight over easy accomplishment of a mission; when Zoro and Sogeking were cuffed together, he wished to help them, so he would not be forced to share his target with Jabra. When neither agent had the key, both agreed that the prey was up for grabs.
Kaku showed great sportsmanship after his defeat where he laughed at Zoro's comment of working in a zoo. He remarked too bad when Zoro passed Paulie's message of "you're fired", handed over his key without Zoro having to say a word. He also appeared to be the only one of the four members undercover in Water 7 who expressed some regret that he could not go back to the way he had been living for the last five years.
Abilities and Powers
Kaku is a highly intelligent and cunning individual, being able to become a master shipwright within a 5-year period merely as a form of espionage and surveillance over his "boss" Iceburg (who CP9 believed to have possession of the blueprints for the Ancient Weapon "Pluton"). He is also skilled at developing or masquerading with personalities: ranging from fun-loving and almost childish to cold and ruthless (the former seems to be his true mentality, while the latter is a product of his assassin occupation).
He is able to move incredibly fast and leap from buildings from amazing heights and distances without a scratch. During his disguise as a shipwright, Kaku uses a variety of pavers/chisels as projectile weapons (used against Luffy in Dock 1). His jumping abilities has earned him the nickname "Mountain Wind" (山風 Yamakaze?) during his time in Galley-La.
Kaku can also function as a lie detector. He demonstrated the ability to tell whether something is true or not by feeling a person's wrist and then tell the truth by determining the speed of the person's pulse.
He is a skilled and creative combatant, as despite having no previous experience with a Devil Fruit, he managed to hold off Zoro largely by making up techniques on the spot, such as folding himself into a cube, using his nose as a battering ram, or using his neck as a Rankyaku medium.
Since Kaku worked as a shipwright during his mission in Water 7, this means he has some carpentry skills. Since he was an evaluator, he has great knowledge about ships. He evaluated the Going Merry  and explained the reasons why it cannot be repaired. Like Rob Lucci, a testament of his skills is that he was able achieve them in five years while others spend their whole life growing their skills and what's more was that this was an undercover job. He was also able to recognize the real Pluton blueprints even when Franky was flipping through the pages quickly.
- Further information: Rokushiki
Kaku is proficient in all six forms of Rokushiki, but his expertise seems to be in Rankyaku, due to his many variations of the technique. With a Doriki of 2200, he is the second strongest assassin in his generation of CP9, which is said to be by far the strongest in the organization's history.
- Further information: Yontoryu
He is also the most proficient swordsman of CP9, being able to use two giant chisels as makeshift swords when he clashed with Zoro in Iceburg's room. During his battle against Zoro in Enies Lobby, Kaku revealed that he is a user of Yontoryu (四刀流 Yontōryū?, literally meaning "Four Swords Style") by using two Shirasaya katanas (or shikomizue) and both legs (with Rankyaku). He wielded both of his swords in reverse, similar to Strawberry and Doma.
- Further information: Ushi Ushi no Mi, Model: Giraffe
When he returned to Enies Lobby with Lucci, Kalifa, and Blueno, Kaku ate the Ushi Ushi no Mi, Model: Giraffe. A Zoan-class Devil Fruit given by his boss, Spandam, which allows him to transform into a giraffe-human hybrid and a full giraffe. As Kaku ate the fruit just after the Straw Hats arrived to Enies Lobby (his Devil Fruit was shown in a chest opened and belonging to Spandam), he did not have full control over it, as seen when he first showed its powers to Zoro where he accidentally transformed into full animal-form, when he intended to go animal/human-form. Jyabura even laughed at the fact that he turned into a giraffe.
When in animal or animal/human-form, he can make further use of Rankyaku, as he gains two additional legs. The power of his Rankyaku is also increased, as seen when he uses Rankyaku: Amanedachi to slice through the whole tower that Zoro and he are fighting in.
His animal/human-form also has a square shaped nose and limbs, because of the shape of Kaku's nose while in human form. He can use this, together with his high speed to create a more powerful version of Shigan, the Bigan, by withdrawing his long neck into his body and then firing it at his opponent.
Kaku's new form was very unusual to him, as he was testing the new form out on Zoro. All his transformations, including the "Square Form," used the same move, and even Zoro remarked that the move Kaku was using was extremely repetitive.
CP9's Secret Mission
Five years before the current storyline, four members of the secret organization CP9 took guises in the city of Water 7. Kaku as part of his mission infiltrated Galley-La Company by applying for a job as a shipwright, in the attempt to retrieve the blueprints for Pluton from Iceburg, mayor and former pupil of legendary shipwright, Tom. Kaku became infamous in the Galley-La Company, known notably for jumping off tall areas, clearing massive distances, earning the nickname: "Mountain Wind" (山風 Yamakaze?) and a respected member of the group. He gained the identity of a ship mechanic and diagnostic. Two other members Lucci and Kalifa became a treenail specialist and personal secretary respectively, while the last member Blueno became a bartender. While gaining the city's trust and respect, they tried to get close enough to take the Pluton blueprints in Iceburg's possession, though cutting no corners in their assumed occupations, as Lucci assured Iceburg when they revealed themselves. Unknown to them, a year later, Iceburg had passed the blueprints to Tom's other pupil: Cutty Flam, better known as Franky.
Water 7 Saga
Water 7 Arc
When the Straw Hat Pirates arrived in Water 7, they needed repairs to their ship. However, due to a tipping off from Admiral Aokiji, a convenience in the form of "Demon Child" Nico Robin presented itself, and they blackmailed her to give a fake assassination attempt on Iceburg's life to frame the Straw Hats, and leave them to be taken to Enies Lobby, under the threat of a Buster Call attack. Meanwhile, the Straw Hats themselves pleaded for Galley-La Company to fix the Going Merry. When Iceburg asked Kaku to perform a diagnostic on the ship, Kaku confirmed that the ship is irreparable due to a broken keel and will have no chance in reaching the next island.
However, at nighttime, an "attempt" on Iceburg's life, frames the Straw-Hats, with Galley-La company attacking them in the middle of a battle between Luffy and Franky, the next morning. During the fight Franky called Kaku Yamazaru ("Mountain Monkey") to mock him. At the evening, this time, the Water 7 CP9 group planned to steal the Pluton blueprints and invaded Iceburg's mansion. The four wore disguises, Kaku and Lucci pretending they were defeated by the assailants by using one of the defeated foremen to wear their gear. However, they realized that the blueprints were not with Iceburg, but learned they were with Franky by reading his pulse, when Lucci deduced he was Cutty Flam and one of Tom's pupils. After this, they left and to leave no evidence to their attack and their identities, they set Iceburg's mansion on fire, hoping to kill him in it. However, in the last minute, Iceburg and the Galley-La foremen were saved by Chopper. However, this was no major setback as CP9 had Nico Robin and know Franky's possible whereabouts.
After discovering Franky's secret hideout, Kaku sent the Going Merry into the midst of the Aqua Laguna and to its apparent demise, further reiterating that although his Water 7 guise was false, his analysis was genuine and the ship cannot sail. After capturing Franky and Usopp, they set out for Enies Lobby on the Puffing Tom.
Enies Lobby Arc
Eventually, Blueno and the others arrive at Enies Lobby. They then meet up with the other members that they haven't seen in years and their boss Spandam. Fukuro then tests the others Doriki and reveals that Kaku has a level of 2200. Then, he and Kalifa were given Devil Fruits by Spandam and under the urging of Lucci, ate them.
Although he was initially going to face off with Zoro, he ended up causing the floor to cave in by transforming into his full giraffe form instead of his half-giraffe form. The two fell into the room where Sogeking and Jabra were fighting, and were involved in that fight as well. Jabra started to break out in uncontrollable laughter after seeing Kaku's full giraffe form. Kaku manages to transform into his half-giraffe form, but this only makes Jabra laugh more hysterically and makes Sogeking accidentally handcuff himself and Zoro together.
All this mocking eventually gets to Kaku and, in anger, he uses an attack that slices the tower in half where it remains lopsided for the reminder of the arc. After a bit of arguing with Jabra on whose prey is whose, even offering to help separate Sogeking and Zoro from their handcuffs by using their keys, though neither had the appropriate key, the two agreed to work together to defeat the pirates and escape the oncoming Buster Call. Zoro however managed to hold them at bay by using Usopp as a sword (moreover having Usopp hold one of his swords while he uses Usopp like a hilt) until Nami frees them of their handcuffs.
As Zoro and Kaku continued their one on one match, it seemed Kaku had the upper hand thanks to improvising with his Devil Fruit and his swordplay until he was defeated by Zoro activating a new power called Asura. Zoro then passes on a message from Paulie to CP9, telling Kaku that he and the rest of CP9 are fired. Kaku expresses regret that he can no longer be a shipwright, and that he genuinely enjoyed the profession. Zoro jokingly responds that he will always have the zoo. He laughs, and gives Zoro his key before he passed out. Kaku's key was the final key to be obtained by the Straw Hats, and also the key to Robin's handcuffs.
CP9's Independent Report
He appears on the third cover in the report, sitting, and apparently severely injured, having been carried by Jabra along the Sea Train tracks.He had arrived at St. Poplar and is shown pretending to be a "giraffe slide" while in his full giraffe form for children to ride, in an effort to help CP9 raise money for Rob Lucci's medical bills.
Afterwards, he was at a café with Fukuro, Blueno, and Jabra waiting for Kalifa and Kumadori to return with the shopping, he along with Fukuro is laughing at Jabra.
Later, he is seen as the scorekeeper while the others are bowling. However, their bowling match is interfered when the Candy Pirates ransack the island, so he and the rest of CP9 quickly dispatch them on their ship. Kaku was shown fly-kicking one of the pirates as the crowds cheered. However, since Lucci crushed the skull of the captain, the crowd was horrified and the CP9 realized they cannot stay in St. Poplar, so they sail off to their homeland, where they watch a new generation of CP9 being trained. Captain Very Good arrives to capture them, but they refuse to let him disturb their old home.
As the CP9 battled, and eventually defeated the Marine troops led by Very Good, Lucci contacted a physically crippled Spandam using a Den Den Mushi, and promised to come for him very soon. With that CP9 began their aim to eliminate their former director by leaving their homeland and setting sail.
- Galley La vs. Big Helmet Pirates
- Kaku, Rob Lucci, Tilestone, Peeply Lulu and Paulie vs Luffy and Franky
- Kaku vs. Usopp
- Kaku vs. Roronoa Zoro
- CP9 vs. Candy Pirates
- CP9 vs. Very Good's crew
Early One Piece
An early design of Kaku had him with a normal nose rather than his long rectangular nose.
Also, in One Piece Green: Secret Pieces, it is revealed that he was supposed to fight Sanji instead of Zoro and partly Sogeking.
Translation and Dub Issues
Kaku's name most likely comes from the Japanese word "kaku" (角 kaku?, literally meaning "angle"), a reference to his rectangular nose.
Although Kaku is 23 years old, he speaks as if he were much older, as he adds the suffix "-ja" to most of his sentences. "-ja" is commonly used amongst old men. He also uses "washi", a term of addressing oneself used by old men.
In the FUNimation dub, to match the "old man" style of talking, he uses old fashioned expressions such as "two shakes of a lamb's tail" or words like "skedaddle".
- He has a giraffe theme, due to his Devil Fruit.
- According to Kaku, children go to a zoo to see giraffes (this was his explanation for saying giraffes were cooler than wolves during an argument with Jabra).
- Zoro giving Kaku Paulie's "you're fired" message is a pun on Kaku's giraffe theme; "kubi" (首 kubi?), the Japanese word used for "fired", can also mean "neck".
- Kaku's birthday was revealed in a Volume 43 SBS to be August 7. This is because in Japanese, 8 can be pronounced as ha, and 7 can be pronounced as na. Put together, these make hana, the Japanese word for nose in reference to his long, rectangular nose.
- Kaku ranked at 16th place in the 4th Japanese popularity contest, making him the most popular CP9 member as well as the most popular direct antagonist.
- Kaku's nickname Yamakaze is probably a reference to the Yamakasi, the first group of parkour practitioners, since he is essentially practicing parkour while jumping across the roofs of Water 7.
- When all of Galley-La were fighting Luffy, Kaku told the Straw Hat Captain that the law had turned its back on him. Ironically, after the Enies Lobby Arc, the government turned their backs on him and his comrades because of Spandam's actions.