Hyperdimension Neptunia, a video game series developed by Idea Factory and Compile Heart, 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..
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 like 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, immature, 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."