|Lives:||D Kingdom (manga, Sailor Moon Crystal); Diamond Kingdom (anime)|
|First Anime Appearance:||Romance Under the Moon! Usagi's First Kiss|
|First Manga Appearance:||Act 4 Masquerade Kamenbutoukai|
|First PGSM Appearance:||None (replaced by Yuka Sakuragi)|
|English Name:||Princess Diamond (dub), Princess D (manga, Viz dub)|
|Actors:||Miki Itou (anime), Kana Ueda (Crystal), Lisa Ortiz (dub)|
Princess Dia was the shy spectacle-wearing princess of D Kingdom (called Diamond Kingdom in the original anime) who appeared in episode 22 of the anime series, Act 4 of the manga, and Act 4 of Sailor Moon Crystal. She owned a famous crystal, which Luna and Queen Beryl thought might be the Silver Crystal, which would make her the Moon Princess. She was briefly possessed by Nephrite's shadow, which influenced her to act on behalf of the Dark Kingdom.
It turned out that her crystal was a statue of herself (in the anime and original manga), or a statue of D Kingdom's first princess (in the revised manga and Crystal), and that she was obviously not the Moon Princess. She was one of the few minor characters to appear in both the anime and manga.
- While Princess Dia herself did not appear in the live-action series, the storyline she was central to did. In that version she was replaced by Yuka Sakuragi, a rich girl who was not a princess.
- Princess Dia looked somewhat like a female Gurio Umino when wearing her thick spectacles. When she removed them she was actually very pretty, but she had such terrible eyesight that this did not happen often. In the manga, this led to the Senshi very briefly wondering if Umino was also attractive without his glasses; Takeuchi, in one interview, said that he was quite handsome without them.