- Banned in China: The second Xbox game was not released in Germany because of
well, you know. That's one the reasons the gore was slightly toned down in the PS3 remake.
- Curiously enough, the game had German subtitles anyway (although they were for other German speaking countries like Austria). That was pretty convenient for German fans of the game, that could import it relatively easily.
- Disowned Adaptation: Itagaki did not like Ninja Gaiden Sigma, going as far as to refuse to sign copies of it. This probably has something to do with the fact that he wasn't involved with this particular version of the game (since, objectively, it's not very different from Black). However, he did admit that it gave PS3 owners a shot at the game. And all of the new features in Sigma were carried over to Ninja Gaiden II at the end.
- Dueling Games: Ninja Gaiden 3: Razor's Edge came out in January 2013 in Europe, just a month before another action game featuring a super-ninja who dismembers his way through a super-equipped military force. It's mostly a coincidence though, as Atsushi Inaba denies any inspiration from Ninja Gaiden 3 (even calling the third episode an "unsalvageable crappy game").
- Genius Bonus: If the name Jaquio is read as if it were Spanish (Ja-ki-o) as opposed to English (Ja-kwi-o) then it strongly resembles the Japanese term "Jaki Ou" meaning "King of Demons."
- I Knew It!: Due to the breadth of shared traits between Irene Lew from the NES trilogy and Sonia of NGII, more than a few fans theorized that Sonia was a modern re-imagining of Irene and that they were the same person (Sonia's bio even hints that her name is an alias). Come Dead or Alive: Dimensions, it turns out that they were right.
- Killer App: The 2004 game and its Updated Re-release, Ninja Gaiden Black, were this for the original Xbox, as was Ninja Gaiden II for the Xbox 360. Meanwhile, the original NES game has been rereleased on the SNES, three times through Virtual Console (for the Wii, Nintendo 3DS, and Wii U), on the NES Classic, and through the Nintendo Switch Online service.
- Name's the Same:
- Ryuken is the Japanese name for Ryu's Dragon Sword. It's also the name of the late 63rd successor of Hokuto Shinken.
- Jashin is the name of the Demon in the Original Trilogy. It can also be the cult of which Hidan is a former member.
- Anyone noticed that Irene Lew's alias - Sonia - is the Allied codename for the Mitsubishi Ki-51 bomber?
- There's Jay's Bar, in which Ryu fights the Barbarian in the Original Trilogy, and J's Bar, a bar in Raccoon City in which 8 unlucky souls find themselves caught in the outbreak.
- No Export for You: The Original Video Animation was never licensed to outside Japan, the only way to watch it is through fansubbing.
- The Other Darrin: English localization just can't get a hold of a voice actor for too long. As of Ninja Gaiden III, there are three different actors for each main release. Troy Baker reprises his role, having provided his voice in Dead of Alive Dimensions. Compare and contrast to Hideyuki Hori, who has been voicing Ryu for 24 years, the first of which was the original Dead or Alive back in 1996. But on the other hand, he was actually replacing Keiichi Nanba, who voiced Hayabusa in the earlier OVA.
- Role Reprise: English-wise, Kasumi is once again voiced by her DOA5 voice actress Lauren Landa. Meanwhile, Janice Kawaye returns to reprise Ayane from NG2
- The Wiki Rule: The Ninja Gaiden Wiki.
- Word of God: According to this interview, the folks at Tecmo were quite unsure on how to translate the video game's title ("Ninja Ryūkenden", which means "Ninja Dragon Sword Legend") for the foreign players, so they opted for Rule of Cool even if it didn't make much sense.
Trivia / Ninja Gaiden