At 17-years-old (16-years-old before Season 5), Leni is the second oldest child of the Loud family. She is very naive and quite ditzy, but she makes up for it with her beauty and kindness. Leni is a senior (a junior in Seasons 1–4) at Royal Woods High School and attends school with her siblings Luna and Luan.
Despite being the second-oldest of the Loud children, Leni is quite ditzy and is very forgetful, absent-minded, and perky. Various examples of her simple-mindedness are expressed throughout the series. In "Linc or Swim," she does not know the rules of the game, "Marco Polo," much to Luan's annoyance. In "Project Loud House," she is shown to be unable to walk and chew bubble gum at the same time. When she's being interrogated by Lincoln and Lucy in "Sleuth or Consequences," she thinks they are interviewing her, and states that her favorite color is "zebra."
Her ditzy nature has also caused her to behave like a child, such as in "Changing the Baby," where she got stuck in Lily's crib, calling it a "baby prison," causing her to bawl like a baby, and then gratefully say "agoo" once Lincoln and Lori got her out; and in "Sitting Bull," where she got an "ouchie" (a term for when babies and young kids get hurt), and is then cheered up by Luan when she hurts herself, which she does to cheer up the children she looks after when babysitting.
Despite being ditzy and absent-minded, Leni's shown to be skilled at fashion designing, wood carving, singing, lock-picking, and making smoothies, which demonstrates that while she may not be very bright, she is creative and artistically inclined. She is also very friendly and gets along well with her siblings.
Leni is arachnophobic. This phobia is most prominent in "Along Came a Sister," where Lincoln brings his class's pet spider, Frances, home. When Leni first sees Frances, she panics and attempts to kill her with bug spray. Later on, it is revealed that Frances is still alive, and Lynn Sr. – who is also arachnophobic – hires an exterminator to dispose of her. Leni faces her fear and cuts off the exterminator, in order to save Lincoln's reputation – once again – showing that she does have a big heart.
Leni has also proved that she can be irresponsible, as shown in the episode "Cover Girls." She agreed to cover for Luna, Luan, Lynn, Lucy, Lola, and Lana, and later passed the task onto Lincoln. However, Leni is shown to be very compassionate, as she was the only one of her siblings to prioritize helping her family get better, as opposed to getting away when the Loud family caught the flu in "One Flu Over the Loud House." In addition, in "No Spoilers," it is shown she is the only person in the family considerate enough in the family to be able to make the perfect surprise party because she pays attention to what people like (excluding the surprise part since she always spoils the surprise because she cannot keep it a secret due to her ditzy and naive personality).
Sometimes, she is too nice for her own good. In "Shop Girl," she let a bunch of shoppers take her stuff and was not even upset about it, saying that she would just make some new clothes out of her old ones. Though her siblings taught her to be tougher, she decided that she likes being nice more, as she gave some of the clothes she bought away to people who needed them more. In "Everybody Loves Leni," she worked very hard to bring her work friends and school friends together. She felt guilty for all the arguing between them and punished herself by missing out on her favorite sale, but her friends decided to get along for her sake.
Leni Loud loves designing outfits and accessories to go with them. Leni's easily distracted by shiny objects, and often walks into walls while talking, but what Leni lacks in smarts, she makes up for in heart. She's the sweetest Loud around!
Leni has long, pale-blonde hair, with side-swept bangs, and three pairs of eyelashes. She is almost as tall as Lori, but taller than all her younger siblings.
Her main outfit is a seafoam green dress, with white frills, and triangular sleeves. With this, she wears red hoop earrings, white slide slip-on sandals, topped with light green bows, and a pair of rounded white sunglasses with black lenses on top of her head.
One interesting note about what Leni wears is that the color of the bows on her sandals change to correspond with what she's wearing. In "Ties That Bind" and "Brawl in the Family," the bows were blue to correspond with the tank top and dress she was wearing. In "Tricked!," the bows were white to match the circa 18th-century dress she was wearing while as Marie Antoinette.
Leni's swimwear is also seafoam green with white frills, only it is a two-piece garment. The top half has two simple straps, while the bottom half is longer than the top, and has four white buttons. Instead of sunglasses, she wears a seafoam green swimming cap, with a white bow tie. She retains her earrings and sandals, even while in water.
Her night attire consists of a seafoam green nightgown, that looks very similar to her regular outfit but sleeveless. She also sleeps with a magenta sleeping mask, but later on, it changes to a blue mask, with an image of closed eyes over it. She retains her magenta mask, and like the blue one, it has the closed eyes image.
Leni's original design depicted her with a light blue dress, snow boots, as opposed to sandals, and a hairstyle that resembled Lori's, but was slightly longer.
In "Hand-Me-Downer," she was seen as a younger girl, but her wardrobe wasn't entirely different. She still wore a seafoam green dress and sandals with green bows on them. The only differences are that her dress didn't have frilled sleeves, and she didn't have her sunglasses.
In "Selfie Improvement," she was seen as a younger girl again. She wore a seafoam green shirt, brown cargo shorts, white socks, and seafoam green shoes.
Leni wears her sunglasses atop her head in every episode she appears in. She only removes them when she goes to bed, showers, goes swimming or goes outside in the snow.
Her sunglasses are white, with two black circular lenses, and a shine going across both of them.
When she was portraying a cat in the family play in "Suite and Sour," her sunglasses were triangular in shape, rather than circular, which looked like cat ears. This means that she owns more than one pair of sunglasses.
There is an animation goof that has occurred a few times, where her sunglasses are missing in one shot, and then reappear in the next shot.
In the alternate dimension where Lincoln has brothers instead of sisters, Leni is a boy named Loni. Like Leni, Loni is ditzy and dumb. Unlike Leni, he is thoughtless, and couldn't care less if Lincoln or his other brothers were hurt.
In the second alternate universe, where it's one girl and ten boys, Loni's shown to be very caring towards Linka, Lincoln's female counterpart—in fact, Loni's the one who makes the offer of him and the rest of the brothers staying with Linka until she falls asleep after they heard her screaming in the middle of the night.
Loni eventually turns out to be a product of Lincoln's imagination as it is revealed Lincoln's whole adventure was just a dream.
After finding a hotel worker's name tag in "Suite and Sour," Leni immediately likes the look of the tag and decides to put it on, fooling every hotel customer that walked by her, as the name tag says "Fritz." When the customers start to treat Leni like an actual worker, Leni decides to work as one too, giving her customers the keys to their rooms, and addressing the customers' complaints. She even tried to kick the Loud family out of their room because of reports from angry customers.
The 11 of Hearts
In the minicomic Deuces Wild! and its animated adaptation, Leni takes on the identity of the superheroine "The 11 of Hearts." She plays the role of one of Ace Savvy's sidekicks. Her signature weapons are heart ties with which she uses to tie up her foes. In the comic, she is summoned by Savvy alongside the rest of his deck to help him and One-Eyed Jack to defeat the gas monster. After they defeat it, they prepare to fight against a garbage monster.
The 11 of Hearts appears once again in "Pulp Friction," along with the rest of the Full House Gang. During her appearance in the episode, she saved Ace Savvy and One Eyed Jack from falling into a shark pit by using her pink bow as a rope.
In the episode, "White Hare," where Lincoln imagined how difficult it is to live with 15 extra sisters, Leni is a rabbit named Blair. Like Leni, Blair is a fashionable rabbit with high knowledge of what clothes are most appropriate to wear. Unlike Leni, Blair seems to be smart rather than ditzy, as there was no moment where she was doing something dumb.
Leni was originally going to be an eight-year-old girl who "didn't know her own strength," before being changed to a stereotypical teenage blonde. Her appearance was also completely different; she was obese, and had brown hair pulled into pigtails.
Her original personality is also reminiscent of Lennie Small from John Steinbeck's novel Of Mice and Men, who was not only mentally disabled, but also a big, muscular man who didn't know his own strength.
She likes to make smoothies and can be really creative when picking out ingredients to use.
Leni says that she likes to brush her hair 50 times a day, but she can easily lose track.
She is the first Loud sister to appear in a title card.
When Leni is seen walking, she almost always has her eyes closed, a big smile, and holds her hands up. A running gag is that Leni bumps into walls when she's walking, a possible result of her walking with her eyes closed.
This was brought up in "Fool Me Twice," when she taught her stunt double how to walk into a row of lockers.
Although Leni and Luan are very close, Leni believes that Luan's hair scrunchie is a "fashion nightmare."
Leni's hair is the lightest shade of blonde of all the blonde sisters, along with Lily.
In the comic "After Dark," during the story "Midnight Melody," it is revealed that Leni is a sleepwalker.
Leni wants to get her belly button pierced, but her father forbids it.
As of Season 4, Leni's nose has a different design, a more rounder shape.
According to episode 20 of the Nick Animation Podcast, Leni's favorite movie is Legally Blonde.
She is similar to the movie's title character, Elle Woods, who also is a ditzy, fashion-obsessed blonde. In addition, they are both much smarter than they first appear, as certain episodes show that she is smarter than her siblings realize.
Her life's work is a six-piece children's jigsaw puzzle.
She is the second-oldest, but the least intelligent of her siblings. Alternatively, Lisa is the second-youngest, but the most intelligent of her siblings.
According to the "Ask Lincoln" section on Instagram, the primary reason that Lincoln likes wearing the color orange is that Leni claims that the color looks good on him.
It is implied that Leni inherited her arachnophobia from Lynn Sr.
Before Leni was born, Rita and Lynn Sr. almost did not have her because Fenton the Fox was driving them crazy..
Lori still had Fenton the Fox when she was one year old, implying that Rita and Lynn Sr. put him in the attic while the former was pregnant with Leni.
Since Season 5, she is the oldest sister of the household while her former roommate is at college. Furthermore, she is currently the second Loud sibling to sleep alone in the house, with the first being Lincoln.
In "Schooled!", she is shown to be good with kids when she accidentally entered Baby Bunker Preschool, she was mistaken for a volunteer and related with the kids on a mental level.
If somebody intimidates her, she will attempt to cope by staring at their left ear and reciting the alphabet. However, she has trouble remembering what letters come after "P"