Helmeppo

Lieutenant Commander Helmeppo is a Marine officer and the son of ex-Marine Captain "Axe-Hand" Morgan. Once a civilian who shamelessly exploited his father's status, he (together with Koby) underwent extensive training under Vice-Admiral Garp to become a full-fledged serviceman, currently holding the rank of lieutenant commander. He is also a member of the secret group known as SWORD.

Due to his actions during his initial appearance, he can be considered a supporting antagonist of the Romance Dawn Arc. He and Koby are also the protagonists of Diary of Koby-Meppo Cover Page Serial.

Appearance

Helmeppo is a lanky, average-sized young man with a distinctive cleft chin and light blonde hair.

Originally, he wore his hair in a bizarre mushroom-shaped style, coupled with flashy leisure suits (and what appeared to be a rubber-band ring on his left hand). After his father was ousted from power, he was "demoted" to a standard Marine chore-boy uniform.

Under the training of Vice-Admiral Garp, he became notably taller and more muscular. By the time he progressed to Chief Petty Officer, he started to wear his hair in a broad ponytail, coupled with a white shirt, pale green vest over it, purple slacks, black gloves, and a rather odd-looking black visor over his eyes.

At his current rank of Lieutenant Commander, he has donned a brimmed white hat and junior Marine officer's overcoat. Unlike most other Marines of similar rank, he wears this coat conventionally (i.e. with arms in the sleeves). 

Personality

During his father's rule over the 153rd Branch and Shells Town, Helmeppo was spoiled and obnoxious, constantly exploiting anyone he could with threats of arrest and execution. Whenever his status failed to protect him, he would inevitably collapse into total cowardice. Even at his worst, however, he was notably sentimental, showing small mercies unknown to Morgan.

He lost his luxurious life that he had under his father's rank after his father was kicked out. He was forced to become a chore boy alongside Koby, whose friendly approaches were turned down. Part of Helmeppo was still loyal to his father which was evident when he cried before his father's execution. However, he later realizes that his father is as brutal and murderous as the pirates, causing Helmeppo to oppose and disown him. This finally cut his last tie to his father and pushed him to change, becoming braver and less of a spoiled brat. Eventually, he and Koby become good friends.

Helmeppo matures by the events of Water 7, even referring to his younger self as "that bratty, selfish son who lived off his father's status". Now a lieutenant commander alongside Koby, he continues his training in the Marines. He was deeply (and comically) upset when Zoro and Luffy did not recognize him.

Helmeppo seems to be more levelheaded than Koby when it comes down to analyzing situations, as Koby is more aggressive. After the time skip, he has developed a penchant for being overly formal, even with Koby.

Abilities and Powers

Physical Abilities

In the beginning, Helmeppo was a typical weakling who relied on his father's status to get whatever he wanted. But after a harsh training regimen under Garp, Helmeppo gained great physical prowess. He was able to jump very high while intercepting Zoro.

After the two year timeskip, he became powerful enough to become a lieutenant commander, and overpower an entire pirate crew by himself with great ease.

Swordsmanship

Helmeppo is considerably skilled in swordsmanship. He was able to force Zoro on the defensive for a few seconds before ultimately losing. After the timeskip, his swordsmanship has greatly increased, able to cause considerable damage to a pirate submarine while underwater.

Weapons

As a civilian, Helmeppo showed some interest in collecting weapons (including Zoro's Meito), but no desire or ability to use any of them apart from a single pistol.

As a full-fledged Marine, Helmeppo's weapons of choice are a pair of kukri, which he keeps at the back of his waist on his belt. He was seen using them against Zoro when they met again in Water 7. However, he was still no match for Zoro.

Haki

Helmeppo has implied that he is able to use Kenbunshoku Haki. He commented on how impressive Koby's Haki was compared to his own, in that Koby was able to sense an underwater attack on the ships of the Prodence and Dressrosa Kingdoms when he could not.