Astro Boy: Omega Factor is a beat 'em up video game developed by Treasure and Hitmaker, and published by Sega, as well as JetterMars Production. The game was released for the Game Boy Advance on December 18, 2003 in Japan; August 18, 2004 in North America; and February 18, 2005 in Europe.
Omega Factor is a beat 'em up game starring Astro Boy. Astro attacks enemies using high-powered punches and kicks, which can also knock enemies into other ones and destroy them as well. Using attack moves slowly fills a gauge at the top of the screen. Once the gauge is filled, Astro is able to perform a special attack; rather than simply helping the player, these are required in some situations. Astro is also able to fly using rocket power, which is also sometimes necessary.
Astro's physical performance improves throughout the game. Every non-player character the player meets scores a point that can be used to improve one of Astro's stats, such as strength or flight speed. This is generally not necessary to beat the game, but the incremental stat increases can make the game easier, as well as allowing the player to find hidden areas in levels.
The game features two difficulty levels in the Japanese version, and three in the North American and European versions. Critics have remarked that the Japanese version is comparatively easier.
The game is divided into two episodes: Birth and Rebirth. The Birth episode follows Astro's adventures and other characters he interacts with, and ends with robots being destroyed by a device called Death Mask, after it determines that the robots are too dangerous to be left alive, leaving Sharaku able to conquer the Earth. In Rebirth, Astro is revived by a being called Phoenix, and has Astro go back to the beginning of the story and try to stop the Death Mask, giving him the ability to go back and forward in time to do so.
- Atom/Astro: The main character of the story. He is a robot boy created by a man called Doctor Tenma. He is based on Tenma's son, who had died in a car accident.
- Prof. Ochanomizu/Dr. O'Shay: A professor who aides Astro.
- Wato Chiyoko: A woman who is friends with Astro; assistant to Prof. Ochanomizu/Dr. O'Shay.
- Detective Tawashi: A detective who has a strong disdain for robots.
- Wally Kisagiri: A detective who joins forces with Astro and eventually becomes one of his most valuable allies.
- Atlas: A robot created by Doctor Tenma based on a person called Daichi. He is considered as Astro's brother.
- Rag: A robot who was used to help a man named Rock become President of Antarctica, but defies him and successfully runs himself. After he was apparently assassinated, he took the guise of the Blue Knight, a warrior dedicated to the salvation of robots.
- Duke Red: A prominent figure, and a defender of robots' rights.
- Nuka: A girl robot whom Astro likes. Has a connection to the Death Mask.
- Drake: A sinister politician who seeks the total destruction of all robots. Initially portrayed as wholly evil, but it is soon found that his profound hatred of robots stems from something more personal; he is the polar opposite of Duke Red.
- Prime Rose: The daughter of Drake.
- Rock: A man who ran for President of Antarctica using a robot copy of him to help, but loses when the robot successfully runs. He later becomes the terrorist Lord Deadcross.
- Sapphire: A Princess of the ancient Mu civilization, who is under attack by a man called Sharaku. After Sharaku is defeated, she and Rock, who came back in time with Astro, help improve the civilization.
- North, Denkou, Brontus, Epsilon, and Pluto: supposedly the strongest robots on Earth.
- Uran/Zoran: A robot girl created by Professor Ochanomizu/Dr.O'Shay, she's Astro's little sister.
- Black Jack: A high-quality doctor who aides Astro.
- Pook: A robot boy who recognizes Astro, despite Astro not also recognizing him. He proves to be a key part in Sharaku's ultimate plan to conquer the world.
- Garon: A robot that Sharaku uses to try to kill Astro. Is powered by Pook.
- Sharaku: The primary villain. Has three eyes, and is attempting to conquer the planet.
- Doctor Tenma: The doctor who created Astro and Atlas. Shows no parental affection for either, rather trying to get them to become stronger robots.
- Phoenix: A legendary bird who can bring people back from the dead, including robots.
- Jetter Mars: A robot who looks like Astro. He was found in Tokugawa Plant while looking for Miri, and teamed up with Astro.
- Miri: A robot who is Jetter Mars' sister. She was found in Tokugawa Plant while exploring, and teamed up with Jetter Mars and Astro.
Omega Factor was developed by Treasure and Hitmaker, and published by Sega and JetterMars Production. During this six-month wait, Treasure took the opportunity to rework some aspects of the North American version of the game. Some level layouts were filled with more enemies, and some enemies were given different attacks. In addition, Treasure somewhat improved the issue of framerate slowdown, and added a new third difficulty level. The game received a rating of "E" (Everyone) from the ESRB and 3+ from PEGI.
Omega Factor received positive reviews, with aggregate scores of 85 out of 100 from Metacritic and 86.72% from GameRankings. GameSpot's Frank Provo stated that "[e]veryone, regardless of age, simply must own and play Astro Boy: Omega Factor – because it is one of the best action games on the Game Boy Advance." GameSpy writer Benjamin Turner listed it as one of the best Game Boy Advance games of the year.
The game was highly praised for its visuals. Provo called the game, overall, "a delight for the senses," and praised the detail and lavish animation of the background and character sprites. Geoffrey Winter of Nintendojo stated that the environments are "beautiful and look as if they were built to be admired, not just walked through." He went on to say that Omega Factor has more seductively detailed visuals than any other Game Boy Advance game. IGN's Craig Harris called it a "technical marvel," especially praising the fluid animation of the bosses, and reserving criticism for the game's occasional framerate slowdown.
The few instances of criticism the game received were mainly directed at the repetitiveness of the levels. Turner listed this repetitiveness, specifically for the shooter stages, as one of the game's "cons." Harris stated that some of the levels "are the absolute pits and feel completely out of place because of their slapped-together feel." 1UP.com's Sam Kennedy stated that the levels are "more of a formality than anything – you casually battle a set of enemies until you reach a boss, which is where the real gameplay begins."
Nintendo Power named this their 38th best game of all time in their final issue, saying that it "captures the essence of Astro Boy perfectly and melds it with developer Treasure's trademark brand of pulse-pounding action."  In 2013, Game Informer listed Omega Factor as one of the "Best Anime and Manga-Based Games" released in English. The game was also praised as "The Best Game since Kingdom Hearts."
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