Fushigiboshi no Futagohime

Fushigiboshi No Futagohime ("Twin Princesses Of The Wonder Planet") is a Shoujo Magical Girl series from the director of Sailor Moon, Junichi Sato. Initially a concept with its own interactive webpage by BIRTHDAY (also known for their Daikaijuu Monogatari games), Hal Film Maker took the idea and adapted it into an anime, which began in April of 2005.

Fine and Rein are fraternal twins who are also princesses of the Sunny Kingdom, one of the seven kingdoms of the Wonder Planet, a hollow planet with a floating sun in the middle. They also happen to be "the most un-Princesslike Princesses ever". Fine (the red-haired one) is a Tomboy with a love of sweet things while Rein (the blue-haired one) is a Genki Girl who loves cute things but gets a little insane when it comes to romance.

Unfortunately, the floating sun is starting to lose its power. As the Princesses of the kingdom that looks after the sun, Fine and Rein are secretly tasked by Princess Grace — the legendary hero of the Sunny Kingdom — to investigate the source of the sun's troubles. And to do so, they get the power to change into super poofy dresses. Don't question it, just run with it. Later takes a decidedly dark turn.

It later got a second series, Fushigiboshi No Futagohime Gyu!, in which Fine and Rein get sent to Princess School in order to receive a certification that will allow them to become Queens. During the orientation of new students, they are presented with a legendary bell that will only ring when a certain person, destined to become the "Universal Princess" touches it. Until this time, the bell has never rung until Fine and Rein touch it, transforming them into newer, frillier, poofier dresses. Meanwhile, a strange dark entity has begun to possess people all over campus, causing them to descend into irreversible depression. Unlike the previous series, it follows a standard Monster of the Week format and delves into Magical Girl Warrior themes instead of the Cute Witch style it originally had (presumably due to the success of a similar format in the second half of the original series). Part of the reason of why it was different was because Junichi Sato left in the beginning of its run, most likely due to Creative Differences. Some cite the sequel as something that should have never existed

This series is notable for its extremely high level of sugary sweetness and for the most impractically poofy princess dresses ever, where the amount of frills is directly proportional to magical power.

This series has examples of:

Adaptation Expansion: There's a lot of this, but for starters, contrary to the original concept's solid seven, the anime went out of its way to introduce a secret eighth kingdom on the Wonder Planet, known as the Ocean Kingdom, guarded by Princess Pearl.
All Girls Want Bad Boys: Fine, at least, really prefers Eclipse/Prince Shade over Prince Bright.
All There in the Manual: The character fanbooks and BIRTHDAY's original webpage gives small details to the characters that aren't revealed in the show. For example, Fine and Rein are both eight years old, Bright received Ruby on his tenth birthday, and Shade received Regina (a desert lizard) at the age of five.
Almost Kiss: Rein and Eclipse nearly share one in the manga... only to be cockblocked by Milky!
Anime First
As Long As There Is Evil: The Black Crystal.
Bandwagon Technique: How Bright, ends up taking over the world
Battle Theme Music: FLIP-FLAP's "Miracle Gemini Gyu" becomes the battle theme for Fine and Rein in Gyu!
Beach Episode : Episode 21, in Gyu!
Break the Haughty: Altezza in the earlier episodes.
Butt Monkey: Tio, and to a lesser extent, Altezza.
Chekhov's Gunman: Naginyo, in the first series, proves to be a stock character who just shows up at random parts in Once an Episode just to sing random songs on his harp while charming the ladies. Then, 20 episodes later, it turns out he was a messenger sent by Princess Grace THE WHOLE TIME.
Clap Your Hands If You Believe: This is essentially how Fine and Rein defeat the Big Bad in both series.
Dancing Theme: The first opening theme, "Princess wa Akiramenai", had a little bit of dancing and the twin vocalists of the song, FLIP-FLAP, also did the same dance in a live-action music video version. Similarly, the first ending theme, "Oshare Fantasy", had a little dance sequence and there was a segment in one of the DVD extras that taught the dance.
Disappeared Dad: All the families in the Wonder Planet are nuclear families... except for the Moon Kingdom, where there is a queen, but not a king. In fact, we don't even know who and if Shade and Milky ever had a father...
Dogged Nice Guy: Auler... not because of the Unusual Ears he has, of course!
Ermine Cape Effect
Evil Costume Switch: Bright, when he is possessed by the Black Crystal.
Everything's Better With Princesses
Everything's Better With Rainbows: The opening scene of every episode in the first season shows a rainbow in space.
Frills of Justice
Genki Girl: Fine and Rein both.
Gratuitous English
Happily Ever After: Of course.
Heroic Sacrifice: Poomo, in the final episode of the first series, not that it lasts.
Hollow World
"I Know You're in There Somewhere" Fight: This happens during a lot of confrontations with Bright near the end of the first series.
Impractically Fancy Outfit
Jerk With a Heart of Gold: Eclipse.
Just Eat Gilligan: Most of the princesses would be doing their kingdoms a service by murdering their parents.
Loads and Loads of Characters
Loser Protagonist: The majority of the princesses win Princess Parties because of Fine and Rein's help, but the two have never won one. This was averted in the manga, where they win the final Princess Party.
Lucky Charms Title
MacGuffin: The whole Grace Stones ordeal.
Oddly Named Sequel: Futago Hime Gyu!, with "gyu" being a Japanese onomatopoeia for squeezing (often used for hand squeezing or tight hugs).
Official Couple: Fine/Shade, Rein/Bright, Altezza/Auler, Elizabeta/Fango, Calorie/Tauri, Milro/Pastel... and that's not even including the kings and queens! Even Milky and Nalro got some Ship Tease before they even learned how to speak!
Paper-Thin Disguise: Eclipse as "Shade."
Peacock Girl
Petting Zoo People: Most of the inhabitants of the Wonder Planet.
Pimped-Out Dress
Power Trio/Three Amigos: Fine, Rein, and Poomo act as a trio throughout the series, although you can substitute Poomo for Lione if you want a more human counterpart. Cue the second half of the series, Altezza replaces Lione's role. The trio formation becomes crucial to Gyu! to the point where the students must create teams of three, hence Team Gemini (Fine, Rein, Chiffon), Team Celeb (Elizabeta, Sasha, Carla), Team Jewel (Altezza, Sophie, Lemon), Team Samba (Lione, Calorie, Asuri), etc.
Prince Charming: Bright.
Princess Classic
Princess Curls: Both main characters.
Princesses Prefer Pink: Fine
Put On a Bus: The writers of Gyu! use this trope immensely. The show introduces new princesses and princes while ignoring even the royal families of the Wonder Planet. In other words, if you're looking for anyone who is not Fine, Rein, Poomo, Chiffon, and Bibin, prepare to be massively disappointed. Even Auler doesn't show up as much as he should have. Alongside of that, even the new princesses and princes are basically ignored after having one episode to themselves — Thomas gets this the worst, as shortly after his Heel Face Turn, he disappears for about 20 episodes, and when he finally returns to the Academy, he is Demoted to Extra.
Requisite Royal Regalia
Royal Blood
Sibling Team
Spell My Name With an "S": Rein's name was written as "Rain" in the first eyecatch of the series, but producer Junichi Sato decided to stick with calling her "Rein" because he didn't want her to be associated with the weather rain.
- Milro has an interesting case since her name was spelled "Mirlo" in the first character fanbook, but "Milro" in episode 19 and in the second character fanbook. One has to wonder if "Mirlo" was a typo or if They Just Didn't Care about the proper romanization of her name. Last, some fansubs write her name out by her literal Japanese pronunciation, "Miruro", but it's not Word of God so it has less validity than her other names.** The fansubs romanized Truth's name as "Toulouse" and Altezza's as "Altessa" before the character fanbook came out with the official romanizations. Some people still refer to the characters by their fansub names.
Stop Having Fun Girl: Altezza takes the "Best Food Princess" competition a little too seriously...** Heck, episode 22 reveals that she trained more diligently for the previous parties than all the other princesses combined.
Sugar Bowl: The Mysterious Star is very cute and friendly.
Suspiciously Similar Substitute: In Gyu!, the vice principal of the Royal Wonder Academy resembles Chancellor Roman from the first series, from the character design to even his voice actors. The same treatment is given to Rarau and Yayan, the vice principal's assistants, who seem to be Expies of Rau and Yan, Roman's mooks, in the first series.
Swiss Army Tears: When Fine and Rein lose their hearts permanently after defeating the Black Crystal Planet, it takes Bright and Shade's Manly Tears to revive them.
The Force: The Prominence
Theme Music Power-Up
Transformation Sequence
Transformation Trinket - The Sunny Luces
What Could Have Been: The writers of the show decided not to focus too much on the Love Dodecahedron between Fine, Rein, Bright, and Eclipse because they felt that romance would draw away some of their viewers.
What the Hell, Hero?: During the Best Sweets Princess Party, Fine and Rein inadvertently destroy Altezza's entry while helping Lione. When they go to apologize to Altezza, Altezza becomes rather pissed instead of remorseful at what they have to say. Fine and Rein end up yelling at her and losing all of their princess levels.
Wheel-O-Feet
Wonder Twin Powers: Although Fine and Rein can use the Prominence and the Feather Mewgram by themselves, they need each other to transform and use their most powerful magic. This is also prevalent in Gyu!, where their twin angel mascots, Pyupyu and Kyukyu, are needed to help them transform.