Sentomaru

Sentoumaru is the captain of the Marines' Science Unit and bodyguard of Vegapunk.

Personality
Since he brags about having the tightest defence, Sentoumaru also claims to have the tightest mouth and refuses to reply to any questions. However, despite his claim, he is willing to tell everyone about himself whenever something related to a question or a event occurs. Whenever he gives away information, he claims he is giving it away freely and not because the person he is talking to asked or was curious about something.

Marines
Sentoumaru refers to Kizaru as "Uncle" (Kizaru no ojiki, a Japanese word commonly used to refer to a yakuza family "father" boss), although the Japanese term used does not mean they are family, but rather the pair are on a high level of respect (despite Sentoumaru shouting at Kizaru for using the wrong Den Den Mushi).

Pirates
Sentoumaru claims that he doesn't "particularly have anything against pirates", but nevertheless fights against the Straw Hats with PX-1 and Kizaru, and is anxious for Kizaru to contact him, fearing that if he does not, all of the Pacifista will be destroyed.

Bartholomew Kuma
Not much is known about their relationship, but Sentoumaru did address the Shichibukai as "Lord Kuma". Any possible relationship may stem from Dr. Vegapunk's research facility (as Sentoumaru is the bodyguard, while Kuma is the weapon)

Powers and Abilities
Sentoumaru is seen carrying a massive broadaxe, but has yet to use it in battle.

As Dr. Vegapunk's bodyguard, he claims to have a world-class guard. He fights similar to Bartholomew Kuma's style, standing like a sumo-wrestler and striking with open-palm strikes, which are strong enough to push back and injure Luffy. Sentoumaru's first named attack is Ashigara Dokkoi, where he smashes his opponents with an open-palm with extreme force. He is also able to run very fast as seen running after Luffy and easily catching up to him, in addition to appearing unfazed by Ussop's giant smokescreen shortly beforehand.

However, despite all this, he claims he is not a Devil Fruit user. May be Sentoumaru is a Haki user, because his move when deflect Luffy's punch is same as Boa Sandersonia's move when she deflect luffy's move too. And so far we know that Kuja Pirates is Haki User.

Sabaody Archipelago Arc
Sentoumaru was first seen on top of a building when Dias attempted to escape his slavery from his Tenryuubito enslavers, although not introduced then. Sentoumaru had been disappointed that Dias could not possibly have survived in the New World.

When Kizaru arrives on the island he attempts to look for his subordinate but is unsuccessful. Later Sentourmaru is seen on top of a building wondering why Kizaru had not contacted him, since the fight had already started. When Sentoumaru finally contacted Kizaru, Kizaru was scolded by Sentoumaru for trying to use a Black Den Den Mushi instead of his Baby Den Den Mushi.

After the Straw Hats defeat PX-4, Sentomaru arrives, revealing only his name in passing, and attacks the Straw Hats with PX-1. Luffy attempts to split up the Straw Hats, but Sentomaru goes after him, Robin and Chopper; PX-1 pursues Nami, Franky and Sanji; and Kizaru intercepts Zoro, Brook and Usopp. Sentomaru knocks Luffy back with his attacks, claiming to have the strongest defense in the world.

After the Strawhats try to escape, he follows Luffy and sicks PX-1 after a wounded Zoro. He manages to best the weakened Luffy physically even without using his broad axe. He is then seen looking surprised at Choppers "Monster" form before he was attacked.

Major Battles

 * PX-1, Kizaru and Sentoumaru Vs the Straw Hat Pirates

Trivia

 * Sentoumaru's name contains the kanji for "peach" (桃) in reference to the Japanese story Momotaro, from which the Admiral names are also derived.
 * His design is similar to that of the Japanese folklore hero Kintarō (also known as samurai Sakata no Kintoki), who was notable for carrying a massive axe and his raising wrestling bears. (possibly showing his close connection to the Kuma-clone Pacifista)