Cash-Cow Franchise: The entire series is Compile heart's flagship title.
Cast the Expert: 5pb. is an Idol Singer just like her Japanese voice actress, nao, who sang the opening themes of the games from the first game to Superdimension Neptune Vs Sega Hard Girls.
Channel Hop: During the franchise's early years in the States, the first three games plus Producing Perfection were published and localized by NIS America, the main US publishers for the Disgaea series. When Idea Factory made their own US branch called Idea Factory International in 2013, the rights for the games along with their othertitles were transferred to them, where all future games would be distributed. Because NISA no longer had the publishing rights for the games, the games they published were swiftly taken off from their website and moved to IFI's. Notably, none of the NISA-published games were released on Steam, since they were licensed by NISA first.
Completely Different Title: The series is known in Japan as Choujigen Game Neptune (lit. Super Dimension(al) Game Neptune) and Hyperdimension Neptunia internationally. Games starting with Super Neptunia RPG would ditch the "[Prefix]dimension" entirely, leaving it as just Neptunia.
Crossdressing Voices: Warechu, a male rat, is voiced by a female in every version — Neeko in the original Japanese language, G.K. Bowes in the English dub of the games, and Sara Ragsdale in the English dub of the anime.
In Re;Birth1, when Neptune, joking obviously, says "Iffy" must mean "I Feel For You" (as in IF loves her), Compa says they should call her "Ai", as that's Japanese for love. IF's Japanese name is "Aiefu" and she's called "Ai-chan" in the Japanese version. (The original Japanese dialogue for this scene had Compa call her "Love-chan" instead).
A running gag in the game is that most people have inexplicable difficulty pronouncing Neptune's name. On one occasion, it's accidentally rendered "Neptunia." This is a Development Gag rather than a form of Title Drop because it's also the case in the original Japanese voice track, where Neptunia isn't part of the title — the last word of the Japanese title for the series is simply "Neptune", after the protagonist, but it was changed to "Neptunia" for overseas release, which this references.
Each game in the series is released a year apart from each other. The only exceptions are Cyberdimension Neptunia: 4 Goddesses Online and Neptunia x SENRAN KAGURA: Ninja Wars, which were released on the same year as their Japanese releases only a few months apart.
The anime adaptation first premiered in Japan on July 12, 2013, and wouldn't get a US release until Funimation acquired the license in 2015, 2 years after its initial premiere.
The Limited Edition box sets regularly consists of an art book that shows some illustrations for the characters (including Concept Art), settings, and cutscenes, a CD for the soundtrack, the cover for the game itself, and some merchandise like a poster. The US Limited Edition box set for Victory has it styled like a lunch box.
As with any game from NIS America, the Western releases of the games tend to sell more copies than their Japanese counterparts. Re;Birth1's Western release is especially noteworthy: Only 1000 copies were made, and nobody was allowed to pre-order. This is presumably a reference to the original game having its first 1000 copies being sold with a pack of Neptune playing cards. Not a good way to do it considering the difference in popularity between the two games, though.
As Steins;Gate wasn't released in North America until after mk2, Kurisu Makise, Mayuri Shiina, and Itaru Hashida ALL made their North American debut in this game as 5pb's Skills.
Superdimension Neptune VS Sega Hard Girls marked the first US appearance of the titular Sega Hard Girls, as their home series and merchandise were not released outside of Japan at the time, and while the anime would get a US release, it was made sub-only; Superdimension Neptune would mark their first English dubbed appearance by proxy.
Gust as a character doesn't actually originate from this series, but predates the series by a long shot as the mascot of Gust's online store, and her first appearance in a video game was Atelier Viorate. But with the relative obscurity of the shop and Viorate never making it overseas, it's common perception (especially in the West) that she originated with Neptunia, even after the shop mascot version ended up going through Divergent Character Evolution and getting a different voice actress.
The first game ran out of money and was mostly unfinished. The second and third games were given a higher budget and received a warmer reception.
Idea Factory International is notorious for their limited budget when it comes to dubbing the games, as only a half of the dialogue in the cutscenes are audible. Compared to NIS America, the former distributor of the series, where almost all of their dialogue is fully voiced due to having a slightly higher budget.
Neptunia Virtual Stars was the first title in the series to not be dubbed into other languages. This is likely due to the fact that actual Vtubers are part of the cast, though the COVID-19 Pandemic making English dubbing harder, in addition to possible budget constraints, may have also been a factor.
Neptunia x SENRAN KAGURA: Ninja Wars didn't get a dub either, though this can be more easily excused as the Senran Kagura games historically haven't been dubbed anyways.
Australia hasn't gotten any games past the first one. If an Australian wants mk2 or Victory, they'd have to import it. Victory eventually got a very small print run down under, and all three games can be purchased from PSN.
The anime's OVA trilogy, "Neptune's Summer Vacation" in 2019, "Nep-Nep Festival" in 2021, and "Little Purple Sunshine" in 2022, have never been licensed by Funimation (now Crunchyroll), who hold the US distribution rights for the anime.
The manga and light novel adaptations, such as ~Megami Tsushin~ and Choujigen Game Neptune: High School, have never received official English translations. English Fan Translations do exist though.
The Drama CDs are usually Japanese only, given their nature of being audio dramas featuring the characters Japanese voice actresses.
No Port For You: The NISA-published games (Hyperdimension Neptunia, mk2, Victory and Producing Perfection) are the only titles to not receive a Steam release.
The Other Darrin: The English dub has had a long history of replacing their voice talents.
In the English dub of VII, Vert's voice actress, Tara Platt, was replaced by Carrie Keranen, who also voices Rom, owing to Platt's unavailability. Keranen has since voiced Vert.
Erin Fitzgerald did not reprise her role as Noire in Cyberdimension due to her participating in the 2017 SAG-AFTRA strike and becoming a union-only VA. As a result, Noire was instead voiced by Erica Mendez, with Mendez becoming Noire's de-facto voice actress in future games.
While Rie Tanaka enjoys her role as Neptune, she also finds the character's high-pitched voice somewhat strenuous to keep up, as Purple Heart's contralto is what she's used to.
Julie Ann Taylor's most famous roles are peppy or kind-hearted young women what with the likes of Taiga Fujimura, Tsubaki Yayoi, and Neptunia's own 5pb.. The shy and insecure but also highly unstable Rei Ryghts is one of her rarer roles. And whereas most of Taylor's roles were of heroines (or in Kokonoe's case, an Anti-Heroine), Rei is the main antagonist of her game.
In contrast to her role as the heroic and friendly Compa, Cristina Vee playing the antagonistic Croire complete with a lower pitch voice was surprising since she's known for playing upbeat heroines like Marinette Dupain-Cheng and Shantae. That's not to say Vee hadn't done these types of characters before and afterwards though.
Recursive Adaptation: In the anime, this pops up when Vert ends up playing Four Goddesses Online, an MMO. A pause screen shows that she's actually playing Victory.
Unspecified Role Credit: The credits only lists the (Japanese) voice actors with their characters. The non-important characters only have the names of their voice actors. This applies to the English dub as well, which only lists the original Japanese voice cast, leading to some characters without English voice actors to this day (Linda, Game Gear, Aneeta Job etc.)
Blanc in the original Japanese dub had a calm, soft-spoken voice that would often switch to a gruffer Tomboyish Voice whenever she was in a bad mood or as White Heart. The English dub, while initially sticking with the former portrayal, gives Blanc a more louder, shrill, sarcastic, and passionate voice that is near identical to her HDD form. She briefly switches back to her more soft-spoken portrayal during her VR scenes in VIIR, as a result of being programmed with her Japanese voice actress in mind.
Vert has a deeper voice in the English dub, sounding more of a mature adult instead of the calm and youthful voice Rina Sato brings to the character in the Japanese dub. Both voices emphasize her Cool Big Sis status.
Uni's HDD form Black Sister gains a significantly deeper voice compared to her normal shrill voice. This was not carried over in the dub, as Sarah Anne Williams uses the same voice for Black Sister as she does for Uni, though she sounds noticeably raspier.
Anri from Sisters has a much deeper voice in the dub.
The series as a whole was originally going to be pitched as an entirely different game about 3 princess sisters and a (male) protagonist, with the intent of collaborating with another company. When the partnership fell down however, the project was retooled into "Neptune" and the rest was history. The game was also supposed to be a Stealth Sequel to Trinity Universe, another collaboration game made by Idea Factory, as opposed to being an original IP, which could explain why the game mechanics used in the first game were previously used in Trinity Universe.
Instead of Neptune, Noire was supposed to be the main protagonist. When Tsunako, the artist of the Neptunia games, drew a sketch of a character that would later become Neptune, the developers liked that drawing so much that they chose her as the main protagonist instead. Noire would eventually get a starring role in Hyperdevotion Noire: Goddess Black Heart.
Blanc and Noire's respective colors were originally blue and red, but were changed to white and black to fit the game's premise.
The prototype that would eventually become Blanc (named "MP Test Girl") originally wore a bow instead of a hat (though that was used as an accessory in the final game). Her timid looking expression also indicated that she was going to be a Shrinking Violet (an aspect later adopted by Rom) as opposed to the quiet but short-tempered goddess we have now.
General Trivia
Some sources claim that Erika Lenhart voiced Rom in mk2, Victory, and Producing Perfection, before Carrie Keranen took over the role starting with Re;Birth1. However, others claim that Carrie has played the role since day one.
, and her first appearance in a video game was Atelier Viorate. But with the relative obscurity of the shop and Viorate never making it overseas, it's common perception (especially in the West) that she originated with Neptunia, even after the shop mascot version ended up going through Divergent Character Evolution and getting a different voice actress.