Excel Saga (Japanese: エクセル♥サーガ, Hepburn: Ekuseru Sāga) is a Japanese manga series written and illustrated by Kōshi Rikudō. It was serialized in Shōnen Gahōsha's seinen manga magazine Young King OURs from 1996 to 2011, and its individual chapters were collected and published in 27 tankōbon volumes . The series follows the attempts of Across, a "secret ideological organization", to conquer the city of Fukuoka as a first step towards world domination. The title character of the series, Excel, is a key member of the group who is working towards completing this goal, while the city is being defended by a shadowy government agency led by Dr. Kabapu.

The manga was adapted into an anime television series by Victor Entertainment. Directed by Shinichi Watanabe and animated by J.C.Staff, the series was broadcast on TV Tokyo from October 1999 to March 2000. TV Tokyo aired 25 of its 26 episodes. The finale was deemed too violent, obscene, and lengthy for broadcast on Japanese television and was only included in DVD release of the series.

Believing the World to be corrupt, the secret organization Across plans to conquer the world. The first step in the plan for world domination is to begin by focusing on one city in order to minimize setbacks. Across consists of the leader of the organization, Il Palazzo, and his young adult officers: the enthusiastic and energetically devoted Excel and the soft-spoken Hyatt, who is prone to fainting and losing lots of blood at a time. Excel and Hyatt live in an apartment building in the city, along with their pet dog Menchi, who they have deemed their emergency food supply. Excel and Hyatt are later joined by a snobbish but equally clueless rival officer of Across named Elgala.

Living in the neighboring apartment are three guys: Iwata, Sumiyoshi and Watanabe, who along with apartment neighbor and co-worker Matsuya, work for the Department of City Security. The Department's leader, Dr. Kabapu, also has a grandiose plan on stopping Across; he has the City Security workers dress in Super Sentai-like uniforms and sends them on different missions. Supporting Kabapu is an inventor Gojo Shiouji who likes little girls, and his gynoid Ropponmatsu, who later is deployed as two models.

The series follows the daily interactions among the two groups. Il Palazzo would send the girls on their missions but the results are usually a failure with some explosive or catastrophic damage to the city. Kabapu would send the City Security workers on some equally ridiculous assignment which would also go wrong. Eventually Il Palazzo and Kabapu become aware of each other's manipulations and escalate their plans. Excel finds herself being replaced by an impersonator who heads the ILL Corporation. Massive amounts of money is spent on elections and politics. Eventually the members of Across begin making appeals directly to the City's citizens before Il Palazzo publicly declares the existence of Across and its intentions to the public. Hyatt is captured and Excel and Elgala are later held in an immigrant detention center before being rescued by Il Palazzo, who begins the new phase of his plans.

The anime adaptation introduces some original characters: immigrant worker turned wandering spirit Pedro; alien mascot-like creatures called Puchuu; and The Great Will of the Macrocosm, the last of whom occasionally resets the storyline. The anime director Shinichi Watanabe cameos as an afro-wearing guy named Nabeshin, and a caricature of the manga artist also makes appearances.

The series was created by Kōshi Rikudō and based on a doujinshi he had previously created while in high school named Municipal Force Daitenzin (市立戦隊ダイテンジン, Shiritsu Sentai Daitenjin). Excel Saga was created as an evolution of Daitenzin in order to develop the character of Excel, as well as to laugh off the vision of a depressed and pessimistic view of the world. Excel Saga is set in Fukuoka City and the names of characters and organizations are derived from local locations and buildings.

Victor Entertainment contacted Shōnen Gahōsha about adapting Excel Saga into an anime, and the two companies approached Rikudō. Shinichi Watanabe was chosen as director. Watanabe added his own alter ego, Nabeshin, and expanded several elements. He says that the Great Will in the manga was "conveyed just as words", and he himself developed its appearance, eventually settling on the "swirling, talking cosmos". He also increased Pedro's role in the story from a single frame in the manga. Watanabe says he was pleased with that aspect of his work, noting that "Pedro's situation was considered unsuitable for broadcast in Japan". The anime production staff was given the freedom to do anything they wanted as long as they kept the theme of the series intact, and Rikudō requested they created a separate timeline; this departure from the original work was acknowledged in-story, with each episode opening with a caricature of Rikudō giving "Nabeshin" permission to diverge from the source material, hence the anime's "Quack Experimental" tagline. Rikudō would later become influenced by the anime series due to its quick broadcast in comparison to the monthly schedule of the manga. The anime makes frequent use of parody and in-jokes as comedic devices, with each episode having a genre-based theme. This extends to the animation, with several characters designed in the style of other works, such as those by Leiji Matsumoto. Kotono Mitsuishi was chosen to play the role of Excel, and Watanabe was impressed with Mitsuishi's rapid delivery of her lines, saying that "she really pushed herself to the limit and beyond". He also says, "at times she was too fast, and there was plenty of time left to match the lip-synch". In such cases, either he would add new material or Mitsuishi would ad-lib. At first Rikudō felt stunned and uncomfortable at hearing Excel speak, but he called the casting "amazing" and was pleased to hear his favourite voice actors read lines from his work.