Ito Nui

Nui was a Trickster found in Ruin No.3 in Parano.

She was a friend of Alice and they came to Parano together, however she wasn't as strong as Alice and ended up felling to darkness and became a Trickster.

She was "killed" by Haruhiro using Resonance and her body was left to rust in the Iron Tower of Heaven.

As a human
According to herself, Nui is an ugly fat woman. She says that she is quintuple cursed, having big bones, thick shin, hard flesh, dark and dry skin. The shape of her face was also bad as she said that she would need plastic surgery to deal with that problem. It's never directly said, but from her Trickster appearance and what she says when making a doll, she likely had short and fatty limbs and neck.

She had a very weak presence, and people would usually not noticed her and even if they did it would usually go nowhere, she did try to use makeup to stand out a bit more but it backfired as she then stood out creepily.

As Nui is really self-deprecating and concern about her weight (she seems to be suffering from bulimia), she may actually not have been that fat or ugly.

As a Trickster
Nui Trickster appearance seems to be warped version of what she imagined to be her perfect body when she was still human.

She is doll-like, her body having the general appearance of an extremely thin human woman, with stick-like limbs and neck, slim to an inhuman degree except for the head. Her hands are even stranger than the rest of her body, each finger being some form of tool used to make dolls. Not all tools were described, but we at least know that she has: scissors (index and middle finger), a curved knife, a gimlet, a chisel, and a bow saw.

While Nui's head seems to be rather normal compare to the rest of her body, her face is barely visible because of her large hat and multiple sunglasses. The one visible thing being her big lisps caked in a red lipstick like substance, so red that it looks toxic.

She has hair but we don't not their color or length.

She wears very little clothing: a small shirt and underwear-like clothe over her breasts. Aside from that, she also wears multiple layers of sunglasses and a hat which, according to Haruhiro, looks like an overdecorated cake.

Finally, once again according to Haruhiro, her voice sounds like "the wind blowing at midnight".

As a human
Nui's main trait before meeting Alice was her self-hatred which came in part from the fact that she was very likely suffering from bulimia, as well as some form of trust issues.

However, meeting Alice seems to have been a big turning point for her, falling madly in love with her. As Alice grew on her she seems to have grown more confident, sociable, and somewhat arrogant, also becoming very possessive toward Alice.

As a trickster
As Trickster, she doesn't really have a personality as it's impossible to communicate with her and she doesn't have memories of when she was human. She seems to mostly stay put in Ruin No.3  where she makes dolls not interacting with the exterior. However, she attacks those who trespass on her territory, pursuing those who manage to flee.

Before Parano
Because of her appearance (having been rather chubby from a young age) and her bland personality, Nui grew up to be someone with very little self-love, a general disinterest for other people, yet yearning for attention. She views her ugliness as the source of all her troubles and wanted nothing more than to become cute. Living in fear of putting on weight (likely suffering from bulimia), one of her escape was doll as they were cute and, unlike her body, could be easily shaped to her liking.

While she yearns for nothing more than to be cute, it wasn't in pursuit of a relationship (as she had no interest in neither men nor women) or for popularity; her goal was to feel pretty, to feel special.

At least before meeting Alice, when they met for the first time, Nui became mesmerized by Alice seeing them as a genderless being with a strange beauty beyond regular human. Feeling a mix of love (not romantic) and hate for someone who had from birth everything she desired; Nui started to try to get closer to Alice.

Gradually they became friend and Nui's became possessive,: she disliked the fact that Alice had other friends besides her, would stalk Alice, and dug in their past to find ways to possibly blackmail them. However, it seems that Alice was at least partially aware of Nui's actions, but let her act that way to some extent.

Finally, everything changed when one day, as the 2 of them were spelunking, they ended up surrounded by haze and found themself in Parano.

Before the events of Level. 14
What happened then is mostly unknown, but Nui ended up turning into a Trickster probably because of Parano's influence on her already fragile mental state, and after some events led to her and Alice being separated.

When she turned into a trickster, she became obsessed whit what had always been her escape from reality: dolls; also turning herself into a doll-like warped version of her ideal self.

Level. 14 Parano-mania
She first appears in the story, when Alice and Haruhiro are sent flying into Ruins No.3 by a dream monster, they crash into one of the town's house and quickly run into one of the dolls "living" there. As the 2 are trying to flee the town they're intercepted by Nui, at first Alice tries to speak to her, hoping that their old friend will recognize them. But it's quickly obvious that Nui can't be spoken with and the 2 sides get into a fight.

Nui is more powerful than even Alice empowered by Haruhiro, but they're able to flee by collapsing a building on her and during the short time when she is buried under rubbles.

While their escape is a success, Nui manages to track them and attack Alice and Haruhiro a second time as they're ascending the Iron Tower of Heaven. This time, however, they're able to beat her, Alice acting as a decoy enabling Haruhiro to sneak on her and use resonance.

As the 2 become one, Haruhiro is able to learn Nui's life story and why she became a trickster, finally using their link to speak and reason her. While Haruhiro was hoping that he could turn her back into a human, Nui chose to kill herself as being a trickster was to her like a long unending nightmare.

After that Alice and Haruhiro cover her corpse and place her near the rusted man so that she can quietly rust here too.

Abilities
As Trickster, her body is heavily mutated, and her magic shouldn't be limited by the 4 categories.

Her main way of fighting seems to be using her doll to attack her target first, before attacking it herself using her tool like hands. Which are powerful enough to counter and cut Alice's shovel's strips of flesh empower by Haruhiro's resonance. Aside from her hands the rest of her body is also very resilient as she easily survived being buried in the rubble of a collapsing building.

The nature of her magic is unknown but likely as something to do with doll making and body modification.

Alice
To Nui Alice is everything she ever wanted to be: beautiful and unique, As such Nui arbor a mix of envy and love for Alice. Those feeling are what pushed Nui to do everything she could to get closer to Alice, and made her more and more possessive of them, leading to Nui stalking and making preparation to blackmail Alice if she ever needs to. It's also important to note that the love Nui as for Alice isn't romantic but closer to a form of fascination, in fact, if Nui "says" that if she could become Alice by killing them she would have done it, but since it's impossible she is trying to be as close as possible instead.

For their part, Alice is aware of Nui's feelings, even knowing that Nui wishes to be them, but they accept it and don't reject Nui. When Nui dies they act in an unusually caring way toward her showing that they did like Nui. Before Parano it seems like they would regularly be harsh on Nui though, but Nui would never retaliate in fear of having Alice distance themselves from her.

Being separated from Alice seems to have been what triggered Nui to become a trickster.

Quotes

 * "If killing Alice would let me become Alice, T'm sure I'd have done it. That was, of course, impossible though." - Nui, Level. 14