Mera Mera no Mi (Generalzer0)

The Mera Mera no Mi is a Logia-type Devil Fruit that allows the user to create, control, and transform into fire at will. "Meramera" is the noise a fire makes when it burns. It is called the Flame-Flame Fruit in the Viz Manga and FUNimation dub, and the Flare-Flare Fruit in the 4Kids dub and FUNimation DVD subs. It was eaten by Portgas D. Ace, but is now presumably back in circulation.

Its powers were first hinted at when Ace visited a town in Drum and apparently caused the snow to temporarily stop falling there for a day.

Strengths and Weaknesses
The fruit's major strength like other Logia types is that it allows the user to produce as well as become the element they control. In this case, Ace is able to create, control, and become fire. With this in mind, Ace is able to create fire-based attacks. He is also able to avoid normal attacks by turning into fire and allowing the attack to pass through him. Turning into fire also has the added effect of burning an opponent depending on the range of the attack.

This fruit's power seems to come to a stalemate when directly challenged by Aokiji's ice powers or Smoker's smoke powers. However, it is weak against Akainu's magma, which causes the user to be burned by it despite their intangibility, making it their natural enemy. Other than that, the user is also affected by the standard Devil Fruit weaknesses.

Usage
The fruit's bestowed powers, as used by Ace, have been used in a variety of ways. Since he left home three years before Luffy and Luffy didn't know that Ace had powers before their Alabasta reunion Ace at the most had his powers for around three years. Ace notably used his powers usually either to fight or to propel his raft. Ace shares Luffy's penchant for naming his techniques, with the only difference being that Luffy adds the phrase "Gomu Gomu No", followed by the specific name of the attack (usually inspired by a certain object or concept). Ace names his attacks in Japanese and they are often made of two-word phrases and are based on different mythologies. During Ace's cover story, the powers of the fruit allowed Ace to rescue a Marine officer and some documents on board a burning ship. Despite being weakened by the Yami Yami no Mi severely during his fight against Blackbeard, Ace was still able to skillfully use the fruit's power to inflict some damage to his former subordinate.

The named techniques that are used by Ace that involve the Devil Fruit are as follows:
 * Kagero (陽炎): Ace shoots a stream of fire from the palm of his hand. This was first seen being used to stop Smoker from catching Luffy. This is called Sun Flare in the Viz Manga and Heat Haze in the FUNimation dub.


 * Hiken (火拳): Ace's apparent signature attack and the source of his nickname "Fire Fist Ace". Ace turns his fist into flames and launches it as a column of fire at his target. This attack is so incredibly powerful that it is able to plow through several ships in one shot. However, it was completely neutralized by Akainu's Dai Funka. This is called Fire Fist in the Viz Manga and FUNimation dub and Heat Fist in the 4Kids dub.


 * Higan (火銃): Pointing the index and middle fingers of both hands at an opponent like guns, Ace turns his fingertips into flames and shoots bullets made of fire from them. This technique was first seen when Ace retaliated against Van Augur's attack. In the Viz Manga and FUNimation subs, this is called Fire Gun.


 * Enkai (炎戒): Ace amasses a large amount of flames around his body (usually by first swinging his outstretched hand around him, summoning the flames) in preparation for an attack. This is apparently the prerequisite technique before Ace can use Hibashira. In the FUNimation dub, this technique keeps its original name, and in the Viz Manga, this is called Flame Commandment.
 * Hibashira (火柱): Used following Enkai,. Ace shoots the collected flames straight upward, destroying a target above him. It can also be fired downwards to clear any enemies that might be below him while he's in mid-air. This technique and its prerequisite technique were first seen when Jesus Burgess threw a hotel at Ace. In the Viz Manga and FUNimation subs, this is called Fire Pillar.


 * Hotarubi (蛍火): Ace creates many small, glowing greenish yellow fireballs that float around an enemy. The idea behind this attack's name is that before he attacks with them, the small fireballs look like fireflies in the air. This move is apparently used in preparation for Hidaruma and was first seen in Ace's battle against Blackbeard. In the Viz Manga and FUNimation subs, this is called Firefly.


 * Hidaruma (火達磨): After using Hotarubi to send the fireballs floating around in proximity with the enemy, Ace sends them all flying into the target(s) all at once, burning them. This was first seen being used in Ace's battle against Blackbeard after Blackbeard performed his initial attacks. In the Viz Manga and FUNimation subs, this is called Fiery Doll.


 * Shinka: Shiranui (神火 不知火): Ace hurls long lances made out of fire. The lances have the combined effect of simultaneously burning an opponent while piercing them. This was first seen being used against Blackbeard when Ace was being pulled forward by the former's power. In the Viz Manga and FUNimation sub, this is called St. Elmo's Fire.


 * Jujika (十字火): Ace puts his index fingers together in a cross shape before launching a cross-shaped column of fire directly at his opponent. In the anime, after crossing his fingers, a cross-shaped ray of light can be seen emanating from the fingers at the target followed by the column of fire. This was first seen being used against Blackbeard after Ace attacked him with Shinka: Shiranui. This attack's name is a pun since "Juujika" refers to crossfire from weapons, yet Ace is making an actual cross out of fire. In the Viz Manga and FUNimation subs, this is called Cross Fire.


 * Dai Enkai: Entei (大炎戒 炎帝): Ace's ultimate technique. After creating great spiraling flames centered on his location before amassing it at a focused point (i.e. the palm of his hand), Ace then turns it into a gigantic fireball resembling the sun and hurls it at his opponent to try to obliterate them. This was first seen being used during the final moments of Ace and Blackbeard's battle. "Entei" is a homonym with "Enkei" meaning "circle," a reference to the attack's shape. In Unlimited Cruise, Ace activates this move by first bending his knees slightly and then placing the outstretched palm of his hand towards the ground (with his other hand gripping the wrist for support), where the flames manifest themselves into a sphere. In the FUNimation dub, this technique keeps its original name, in the Viz Manga, this is called Great Flame Commandment: Flame Emperor, and Flame Commandment: Flame Emperor in the FUNimation subs.


 * Enjomo (炎上網): Ace creates a circle of fire around a selected area, preventing anyone from entering or leaving it. This was first seen being used in a flashback against the Marines in Alabasta under the command of Smoker, and was named in a flashback against Whitebeard. In the Viz Manga and FUNimation subs, this is called Flame Fence.


 * Kyokaen (鏡火炎): Ace releases a wall of fire to block an attack. This was first seen to counter Aokiji's Ice Block: Pheasant Beak, the two attacks canceling each other out. In the Viz Manga, this is called Mirror Flame and Flame Mirror in the FUNimation sub.

Trivia

 * So far, the Mera Mera no Mi is one of the few Logia known to be inferior to another outside of the Yami Yami no Mi.
 * The idea of a Devil Fruit that would allow someone to use fire was first brought up when Morgan explained what Devil Fruits are.