The other twin princess of the Sunny Kingdom, Rein adores dressing up and gets starry-eyed over romance. She also loves scary things and is more emotionally stable than Fine. Just like Fine loves her cake, Rein has eyes for Bright.
Distressed Damsel: This basically sums up a lot of the Ship Tease scenes between Rein and Shade. Just strike her with a Distress Ball and he'll come running, although this can be justified with the fact that Fine is more athletic than Rein.
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.
Demoted to Extra: Lione seemed like she would be part of the main cast from her appearance since she's the first princess Fine and Rein befriend and she was one of the few who received an Image Song. By the middle of the series, she started appearing infrequently and is even grouped with Sophie and Milro.
Tio is the prince of the Meramera Kingdom and Lione's younger brother. He swore on his life to protect Fine and Rein, but he hasn't exactly done that yet. Later, he becomes Shade's self-appointed apprentice to learn his ways.
Ascended Extra: In the second half of the first series, Tio decides to follow Shade's footsteps and accompanies him on his journey.
Badass Longcoat: Sure, Tio gets a trenchcoat in the second half of the first series, but he's still not as badass as Shade.
Butt Monkey: In almost all of his appearances during the first half of the first series, something always goes wrong so much that it becomes a Running Gag. He gets better... sort of.
Once an Episode: Tio tries hard to help Fine and Rein in every single episode during the first half of the first series, but something always goes wrong. Some of his encounters result in A Twinkle in the Sky.
Altezza is the haughty princess of the Jewelry Kingdom who initially dislikes Fine and Rein on-spot. She's boastful and arrogant, but shows her more introspective sensitive side when it comes to her older brother, Bright, whom she looks up to.
Ascended Extra: Altezza was nothing more than the Alpha Bitch in the beginning of the series, but during the second half, she accompanies Fine and Rein on their journey and even gets a costume upgrade.
Big Brother Worship: Altezza admires Bright greatly to the point that sometimes she gets annoyed when his attention is focused on someone else. This also causes her to be distressed during the second half of the show when Bright succumbs to The Dark Side.
Bright is the prince of the Jewelry Kingdom and is known as the no. 1 idol in the Wonder Planet. He's patient and somewhat of a pacifist, and despite that all the girls adore him, he loves Fine out of them all. This makes him feel threatened when Fine starts hanging around Eclipse...
Shade is the prince of the Moon Kingdom, but masquerades under a secret alias known as "Eclipse." He prefers to carry out his plans in the shadows and becomes somewhat protective over Rein when she is in danger.
Code Name: Shade goes under the name "Eclipse" when he's out of the palace in his trenchcoat guise until the second half of the series when Fine and Rein realize who he is. This trope is disregarded in the manga, where "Eclipse" is really his name.
Batman Gambit: The Henchmen pull several in their Team Rocket Wins episode, among others. First, they know Bright is suspicious of Eclipse and use that to lure him into a trap. Next, they kidnap Milky because by then they know Shade is Eclipse and thus will keep him distracted for a while. Then, they put Fie and Rein into a position where they have no choice but to use the Prominence...while having the machine that can steal it at the ready. Finally, they send Bright into a Bottomless Pit as another distraction for Shade. And that's not even getting into the other gambits they've used throughout the earlier episodes...
When Fine and Rein mistook them for working with Eclipse, two of them overheard it and played along with their assumptions, referring to him as their "boss" and keeping Fine and Rein suspicious of him.
Then when they're trying to steal the Prominence, they take care to stay out of the way and out of sight while they do their work; only Shade/Eclipse's intervention prevents them from succeeding, though they did manage to take a small bit before being stopped once.
Hostage For Macguffin: They threaten Bright's life to goad Fine and Rein into using the Prominence. Subverted in that they still use Bright as a means of distracting Shade and successfully escaping with the stolen Prominence.
Malevolent Masked Men: The Henchmen. Never once do we get to see their faces other than their eyes and some of their skin; the rest is hidden by a hooded robe and mask.
Take Over the World: Roman's main goal. He doesn't succeed and is absorbed into the Power of Darkness when he's outlived his usefulness.
Team Rocket Wins: After several episodes of trying and failing, Roman and his Henchmen hatch a plot to finally take the Prominence. One Henchman disguises himself as Shade and lures Bright into a trap to use a bait for Fine and Rein. Another kidnaps Milky to distract Shade until its too late. the rest hold Bright and use a machine to suck out the Prominence when they force the girls to use it to save Bright.
Spell My Name with an S: Confusion has been abound as to how exactly Milro's name is spelled. In a letter in episode 19 of the first series and the second character fanbook, her name was romanized as "Milro." The first fanbook spelled it as "Mirlo", but it seems to have been a mispelling. The fansubs romanize her name via the Japanese pronunciation, "Miruro." It's commonly accepted that "Milro" is the right spelling and "Mirlo" was just an error that was subsequently corrected in the second fanbook.
Unusual Ears: Milro has bear ears in the anime and ice crystals for ears in the manga.
You Shall Not Pass: She put herself in between a swarm of locusts and Altezza's roses in order to protect them during the Best Flower Princess Party, getting crowned best princess as a result. She's concerned about it now that she's no longer in the loser club with Altezza.
Chiffon is the six-year-old Child Prodigy princess of the Mathematics Planet and is also the president of the student council. She quickly befriends Fine and Rein when they enter the Royal Wonder Academy and teams up with them to form Team Gemini. Since she is used to the strict school policities working against teamwork, she becomes interested in the twins' methods and the concept of friendship.
Late-Arrival Spoiler: The leaked character designs for Gyu! outright says that Thomas was the former prince of the Walpurgis Planet. This was a huge part of his backstory and why he was the villian for the first arc of the show.
Bibin is a student of the Black Planet Academy and wishes to be crowned as its queen someday. She works with Ed-chin under the orders of the principal to ruin their rival school, the Royal Wonder Academy.