Hyperdimension Neptunia is a video game series developed by Idea Factory and Compile Heart that features a wide array of fictional characters originally created by Naoko Mizuno and designed by Tsunako and Minamitsu. The original game centers around Neptune, one of four goddesses who adventures in a world where she can recruit other characters to form a party. Some of the supporting characters are playable depending on the title and also whether it is a remake or an option as downloadable content. Some characters also start as antagonists, and there are a regular set of villains. Most characters are based on and named after the video game consoles, video game developer companies or publishers. The characters have been commented on by game reviewers who had mixed feelings about their designs, personalities and voice acting.

Conception and development Naoko Mizuno, the creator of the Hyperdimension Neptunia series described the origins of the game and its characters: "First and foremost, I realized there were no games on the market that actually dealt with or parodied the game industry itself. The second thing is that, at the time, characters that changed—that took on different forms—were really popular, but there were none that were cute girls." She developed Neptune as a parody of the game industry with the fictional scenario where Sega was still attempting to reach the top of the console business. In looking back at the games, Mizuno said that she would have liked to have had the characters fully voiced, but that the editing in of new scenes and content made that impossible.

Executive producer Norihisa Kochiwa said that character designer Tsunako had developed some designs but had run into complications. The company considered partnering with another company but it did not work out. At the end of 2009, Tsunako had changed up the character designs and color scheme so they fit within the world's setting. Kochiwa said "Had that collaboration been realized then Neptunia would have never been born." Director Shingo Onodera said that "the game was originally supposed to be about 3 princess sisters and a main character. I came in right around when that project was halted and turned into Neptunia."

Mizuno created a new group of main characters for Mk2 in response to the moe subculture trend, especially the concept of the younger sister. "The younger sister characters, like Nepgear, are still inexperienced, and not fully grown compared to their older sisters. One of the reasons behind creating such heroines was that I wanted to depict the younger sisters' adorable efforts to grow strong and mature enough to save their older sisters and Gamindustri." She also noted there are no male main characters in the series: "I say this because I know; I'm a woman myself. It's so much fun to have private girl talks and have some girl time without boys around."

The character design was done by Tsunako, with another designer named Minamitsu joining the team starting with Victory. Minamitsu had been working on some other otome games, but regards Victory as her first major title. Kochiwa has remarked that working on Neptunia not only from the art and game system aspects, has affected Compile Heart's other titles. Tsunako said Victory was a turning point for the franchise as it helped solidify the relationships among the sisters.

The anime adaptation contributed to the Neptunia character design and development as it presented the characters from a different perspective. Tsunako said "the animators did a great job so as a designer I feel like I was able to learn from them as well." Onodera said "Being able to observe and learn how people from a different industry handled things like direction, script-writing, building tension, plus visualizing characters and their personalities helped me to see what was lacking in the original Neptunia." Onodera also credits the anime and Mk2 for inspiring them to do the Re;Birth versions.

In deciding what maker characters to include, the team worked with Compile Heart and their relations with other companies. The inclusion of Tekken allowed for more characters to cross over from other franchises such as Millionaire Arthur and God Eater.

Main protagonists The main protagonists are goddesses that represent consoles or portable hardware brands in the video game industry. Their normal interacting form is that of a girl, but during combat, they can transform into a more powerful "HDD Mode" of themselves.

Four CPUs

The Console Patron Unit (CPU) is a goddess character in the world of Gamindustri, each of whom is named after a video game system and is charge of a domain. Director Shingo Onodera said that in creating the scenario for the first game, the three goddesses had lacked something in their personalities so they gave each of them a gimmick.

Purple Heart

The primary playable character in most of the video game titles in the franchise, Neptune is the goddess of Planeptune, and is named after and represents the cancelled Sega Neptune. She has short purple hair, purple eyes, and cross-shaped hair clips that resemble the directional keypad of the console controller. In her NIS America profile, she is described as energetic and optimistic, but "tends to drag others into her problems without realizing it." However, her personality changes once she transforms into Purple Heart, taking on a much more serious and mature character with long purple hair styled in two braids, blue eyes, and a black one-piece swimsuit. In Mk2 her youthful appearance and personality in contrast to her younger sister Nepgear have strangers confusing her as the little sister. In the first game, she is banished to the mortal world and loses her memory, and thus assembles a team of girls to fight monsters in Gamindustri. In Mk2 (and Re;Birth2), she is a supporting character who is held captive in the Gameindustri Graveyard while the player assumes her sister Nepgear's role in rescuing her. She returns to being the starter playable character in Hyperdimension Neptunia Victory where she is sent to the alternate V dimension. In MegaTagmension Blanc, she and Blanc collaborate in making a zombie film. In Neptune vs Sega Hard Girls, she is at war with Saturn (from Sega Hard Girls) when the history suddenly changes and her spirit then possesses IF's motorcycle. Neptunia creator Mizuno said that Neptune is her favorite character from the series because she is "energetic and bright to the point of idiocy". Mizuno also liked her jumping action catchphrase "Like a kangaroo!" from the Victory title.

Black Heart

The goddess of Lastation, she represents the PlayStation 3. She has red eyes and long black hair styled in twin tails. According to game director Shingo Onodera, Noire's original color scheme was red, but was then changed to black. Her NIS America profile describes her as hardworking, polite, an "ideal goddess", but that she tries too hard sometimes, "cares a lot about what others think of her and seems to harbor many secrets about herself." Director Shingo Onodera said that Noire was given a gimmick of being a cosplayer. Onodera also noted Noire's remark to herself of not having any friends to form a band had resulted in being painted as the friendless character. As her transformed character Black Heart, she has long white hair, blue eyes, and a black suit. In the original game, she does not get involved in the story until the end of the game, however, in Re;Birth1 she becomes a playable character. She is described as competitive, tough, and aggressive, and is sometimes involved as an opponent to the party in the game. In Mk2 she is described as righteous but not the most flexible person, and a bit of a tsundere towards her sister Uni. In Victory, she appears in the V dimension, but has not become a CPU. She also has a friend named Plutia. In her transformed state though, she likes her newfound freedom and acts troublesome and uninhibited.: Within the "V dimension" of Victory, her appearance resembles of the original PlayStation. In 2011, Noire won Compile Heart's Neptunia character popularity poll, and became the starring character of a spin-off game. In Hyperdevotion Noire: Goddess Black Heart, she and the other goddesses are presented in chibi style and interact with new characters in a world called Gamarket.

White Heart

The goddess of Lowee, she represents the Wii. She has short, light brown hair, and is described as shy and bottles her emotions, occasionally leading to violent outbursts. According to game director Shingo Onodera, Blanc's original color scheme was blue, and was then changed to white. As White Heart, she has long light blue hair in long sideburns, and a white suit. In that form, she is also quiet and inexpressive. Onodera gave Blanc a hobby of being an avid reader. Onodera had planned for Blanc to be the lonely character but reception to Noire's remark to herself about not having friends changed that direction. In the first game, she dislikes Neptune, and she does not get involved in the story until the end of the game, however, in Re;Birth1 she becomes a playable character. In Victory, Blanc appears in the alternate V dimension where she still has the same personality, and is still a CPU of Lowee, concerned about the developing nations of Lastation and Planeptune. However, her White Heart persona is angry and impulsive. In 2014, Blanc was the winner of the second Neptunia character popularity poll. She is the starring character of MegaTagmension Blanc + Neptune VS Zombies. In that title, she and Neptune are making a zombie movie.

Green Heart

The goddess of Leanbox, she represents the Xbox. In her human form, she has long blond hair, blue eyes, and a polite, feminine personality. She is popular among her people, but is a hardcore gamer whose playing sometimes interferes with her duties. As Green Heart, she has long, light green hair styled in a ponytail, soft speech, and a laid-back attitude. In the first game, she considers Neptune her nemesis. In the original game, she does not get involved in the story until the end of the game, however, in Re;Birth1 she becomes a playable character. In Mk2 it is revealed she does not have a younger sister, and acts more maternal around the other CPUs. In Victory, she appears in the alternate V dimension, where she tries to invade the other continents while they are fighting each other. She is also more proud of her breast size. Her transformation persona Green Heart in this title is more mature than her character in the other games.

CPU Candidates Each of the nations in Hyperdimension Neptunia mk2 has representatives of the goddesses called CPU Candidates, which turn out to be their younger sisters. Their item counterparts are portable handhelds in contrast to the home console references of the goddesses. Of the goddesses, Vert does not have a younger sister, while Blanc has two younger sisters.

Purple Sister

The main character in Hyperdimension Neptunia mk2, she is the younger sister of Neptune. She has light purple hair, and wears a white sailor uniform with purple trim and a yellow kerchief, and a single cross-shaped hairpiece. She is described as very well-behaved and studious, in contrast to her sister who is energetic and compulsive. She transforms to Purple Sister where she wears a purple and black bikini with similar stockings (pre-Hyperdimension Neptunia Victory). She represents the Sega Game Gear. In Mk2, IF and Compa free Nepgear and they form the main adventuring party to rescue her sister from the Gamindustri Graveyard and save the world from the ASIC organization. In Victory she follows her sister Neptune to the V/Ultra Dimension, but as she is not the main character anymore, she feels like she is a punching bag and put down by the others (as well as the game in some cutscenes). As Purple Sister, she has long purple hair and a white one-piece swimsuit-styled uniform.

Black Sister