Lady Rainicorn

Lady Rainicorn is a rainicorn and Princess Bubblegum's loyal steed, best friend, and companion. She is also Jake's girlfriend, and sometimes follows Finn and Jake on their adventures. She speaks only Korean, using English only when equipped with a Universal Translator (however, she is shown to have spoken a bit of English in "Lady & Peebles"). Princess Bubblegum and Jake are the only other beings in the Land of Ooo, besides Lady's parents, that are shown to understand Korean. In "Lady & Peebles," Lady revealed that she is pregnant; this was confirmed by Princess Bubblegum.

Appearance
Lady is a long unicorn-like creature. She has rainbow colored stripes along her body, a bleach blonde mane, and big round eyes similar to Jake's. She also has a single white, sharply-pointed horn. Her mom has a long body like hers, unlike her father. This means that she inherited her length from her mother, since in the episode "Her Parents" her mother and father don't find it odd that Jake can stretch or is long like the females before they know he is a dog. Because Ethel's body is longer than Lady's, and Bob's body is much shorter, it is also possible that Lady has inherited both traits resulting in a body length that is in-between (longer than Bob, shorter than Ethel).

Abilities
Lady has the ability to fly, phase through walls, and can use her horn to change the color of anything she wants. In the episode "My Two Favorite People," Lady Rainicorn explains to Finn that she can fly because her body can intercept beams of reflected light from the sun and "dance around" on them. In the same episode, she is shown to live in a stable in the Cotton Candy Forest. Like her parents, she can fire a chromatic light beam from her horn, which seemingly hurts. Also, Lady can stretch longer or shorter as you can see when she lands. She may have limited Stretchy Powers. It is revealed in "The Creeps" that she can phase through walls and also carry people while phasing. She can play the viola, like Jake. She also has the power to meld people into her being.

Personality and traits
Lady is laid-back and likes to interact with Jake and Princess Bubblegum. She is considered Princess Bubblegum's companion, like Jake is Finn's companion. She does not speak Korean in the origanal short; she only makes soft cooing sounds (or, near the beginning, hysterical screaming coos). However, Jake seems to understand what she says when he talks to her. She believes she is smarter than Jake. She may also have a fondness for Power Ring although she seems to have no fingers.

Lady Rainicorn, unlike both of her parents, doesn't wear a universal tranlator. It's possible that she chooses not to because her closest friends, Jake and Princess Bubblegum, both speak Korean. It is worth noting however, that Lady Rainicorn understands English, but either cannot speak it or chooses not to. This is obvious because of the fact that neither Jake nor Princess Bubblegum speak Korean when talking to her.

Jake
On the official website in Lady's description, it says Jake is her boyfriend and that they get along so well because of their common interest in the viola. This relationship began in the short when he and Lady Rainicorn were flirting and sharing interests. At the beginning of "Slumber Party Panic," she is shown being playfully chased by Jake, and later in the episode, they both seem to very much enjoy playing "Seven Minutes in Heaven" (which is a game where two people are locked in a closet together to kiss for 7 minutes, sometimes leading to other things). In "My Two Favorite People," Lady recalls a time when she and Jake ran naked through a farmers field, causing Jake and herself to blush which may indicate some level of intimacy in their relationship. In "My Two Favorite People," Jake is torn between his desires to go adventuring with Finn and hanging out with his girlfriend. Lady later says she loves Jake "because he's an idiot" and that he makes her "feel like a genius." In "Video Makers," Jake gets very jealous when Mr. Cupake flirts with Lady and becomes violently protective of her. The relationship appears to be rather serious, as he also was worried about his impression on her parents and even went to say he was studying Rainicorn history for their future children. Lady's mother Ethel referred to Jake as hers and Bob's future son-in-law, hinting that she can see them getting married. In Go With Me, Jake takes her to the movie night and they ended up making out through the whole movie night. In the episode "Burning Low," Jake explains to Finn about "tiers" in relationships and is talking about his relationship with Lady Rainicorn in the process. Jake's implications in the explanation indicate that he is very intimate with Lady. In "Lady & Peebles," Rainicorn reveals in English that she's pregnant.

Princess Bubblegum
Lady is usually seen with or near Princess Bubblegum in the Cotton Candy Forest in the Candy Kingdom. In the "Animated Short," she shows great concern when the princess is abducted by Ice King, and even tried to rescue her from him. She is sometimes described as the princess' pet. In "What Have You Done?," Lady flew the princess to the Ice Kingdom so she could ask for Ice King's help in ending the plague in the Candy Kingdom, and showed great disgust at him when he mistook their pleas for help for flirting. Lady even speaks to him at this time, saying "Verily, you are a creature unworthy even of my lady's disdain." When Lady got injured by the eyes in "Lady & Peebles," Princess Bubblegum showed great concern for her.

Finn
In the beginning of episode "My Two Favorite People," Lady Rainicorn and Finn's relationship is awkward because of the language barrier. Attempting to fix this, she helps Finn and Jake recover the Universal Translator at the bottom of a lake guarded by Lake Knights. Finn is impressed by Lady Rainicorn's ability to fight and finds the translator's 'Old Man' voice option amusing, so they soon become friends. Jake gets rid of the Universal Translator, but any persistent issues Finn has with understanding Lady Rainicorn have yet to be mentioned.

Ethel
Ethel Rainicorn is Lady's mother, who appears in "Her Parents." She is very shy to everyone but Jake, Bob, and Lady. She referred to Jake as her and Bob's future son-in-law.

Bob
Bob Rainicorn is married to Ethel, and is Lady's father. Bob appears in "Her Parents," and is very impressed with "Rainicorn" Jake.

Mr. Cupcake
Mr. Cupcake tries to impress Lady Rainicorn by flexing his muscles in front of her in "Video Makers." Although she blushes, she tells Jake not to take it seriously.

Trivia

 * In one room of the candy-castle, there are two pictures of Lady Rainicorn on the wall: One of her upper half, and one of her lower half.
 * Two Rainicorns (both of which look like Lady) appear in the Double Rainbow promo.
 * Her original name was "Lady, the Rainicorn."
 * In the animated short, she spoke in a type of gurgling language instead of in Korean.
 * Other aspects of the Rainicorn people seem to be subtly based on Korean culture and history such as the Korean War, Korean games, and Korean delicacies.
 * In "The Real You," Princess Bubblegum is seen in the beginning with a yellow t-shirt with a red Rainicorn on it.
 * Lady Rainicorn has a gender-swapped counterpart in the Ice King's fan-fiction: Lord Momochromicorn.
 * Her favorite drink is iced latte as shown in "Video Makers."
 * In "My Two Favorite People" Jake refers to her as "the rowdy queen."
 * In "Apple Thief" Jake cooks Finn traditional Korean food that Lady Rainicorn taught him how to make.
 * Despite being based on a rainbow, Lady Rainicorn's body does not display any orange, but in the animated short she had orange on her body.
 * She likes toads.
 * In "Burning Low," Jake implies that her stomach is 15 feet long.
 * In "Card Wars," it is revealed that Lady Rainicorn used to play Card Wars with Jake, and it made her mad that Jake always won the game.
 * She can speak some English words, as shown in "Lady & Peebles": "Ice King," "Jake," and "I am pregnant!"
 * As shown in "Lady & Peebles," five small dots and two larger dots on the heart monitor. Lady is pregnant, and the five dots indicate her unborn children.
 * She is the only main character to become pregnant.
 * She has nightmares about half-dead corpses hurting her family.
 * In "My Two Favorite People," Lady is wearing power rings, even though she does not appear to have any fingers.
 * In a Cartoon Network 20th birthday bumper, she is referred to as Princess Rainicorn.
 * Lady's colors are in reverse order when compared to a normal rainbow.