Yume Nikki is a strange game which has no dialogue and an unique art style.
The creator of the game, KIKIYAMA, stated on their website that the game is meant to be an exploring game with a "dark atmosphere" but without plot or purpose. Still there are themes in Yume Nikki that fans gathered together to create different theories about the characters and locations. Those themes are gathered here.
A theory unique to a character, such as them being a possible reference to something or having a specific theme may also be found in the Trivia section of their character pages.
Themes of Isolation
Madotsuki does not leave her apartment for the entirety of the game. When the door in the real world is interacted with, she shakes her head, making it impossible to exit it. In her dream world, she can not only leave through said door but is able to access the different dream locations through similar looking doors in The Nexus. This can mean that she has a desire to explore, is however not able to do so in the real world and thus feels comfortable to do it in her dreams.
In her dream world, the themes of isolation and loneliness continue. There is no dialogue, most NPCs ignore Madotsuki and only few NPCs turn to her when the player tries to interact with them. The locations themselves feel isolating and lonely, thanks to being large and often looping, with, especially in the original locations, only few points of interests. The somber soundtrack of the game also contributes to this.
Throughout the game Madotsuki encounters tall girls (called Toriningen by fans), who are considered enemies in the game due to their nature of trapping Madotsuki in inescapable locations when in a "lunatic" state. They also have the characteristic of having a group dynamic that goes beyond other multiple identical NPCs spawning in one location (such as the Wheelies).
The most significant example of this is The Toriningen Party, where a group of Toriningen have a picnic together in The Wilderness, while dancing to cheerful music. This party cannot be accessed, as the plants of The Wilderness hinder Madotsuki from approaching any closer. This is commonly interpreted to tie in with a theme of social anxiety or isolation regarding Madotsuki. Other examples being all Toriningen going into the lunatic state when you use the Knife on one of them, or the Toriningen in the Bed Room, who is implied to watch over the beds, activating the ああああああああ event when you use the Knife on her, a much more severe reaction than usual. It is notable that the NPCs thought to be the enemies of the game act as a team while Madotsuki herself is a sole figure.
There are furthermore characters that seem to share Madotsuki's theme of isolation. Said characters are:
- Poniko, who is the only character of The Pink Sea and similar to Madotsuki, never leaves her room of which she seems to be the only inhabitant.
- Mafurako, who is the only NPC roaming around Block World, and prefers to teleport to a random spot far away from Madotsuki when teleporting her back, with the exception of Madotsuki being in her snowman form, which makes Mafurako always teleport next to her.
- Mars-san, who can be found in the underground area of Mars, which can only be reached by crashing a spaceship into Mars and then using an effect to access the tiny hole to the underground. This exit compared to the size of the character themself make them seem trapped, as it is impossible for even Madotsuki to enter if she is her normal size.
Another important encounter in the dream world that may point to a theme of isolation is Closet Madotsuki, a sleeping version of Madotsuki hidden in a closet in The Checkered Tile Path.
Relating to this may be the Hikikomori phenomenon, in which reclusive teens or adults abandon social life completely.
Themes of Anxiety
The theme of being watched seems prevalent in Madotsuki's dreams such as eyes following you in Dense Woods, Barracks Settlement and more on the way to the Witch Effect.
Hands are also scattered throughout the game ranging from a large theme of one world to appearing a few times within another. Some examples being the staircase lined with reaching hands on the way to Seccom Masada-sensei's spaceship, sprouting out of the ground in the Eyeball World and in the White Desert. The room Uboa teleports you to has a nightmarish landscape where a monster with multiple hands grasps hills in the background. The implication may be that Madotsuki dislikes being touched and prefers a great amount of personal space.
A character who may tie into this is Organoid, who is the only NPC to swiftly teleport away upon approach.
Body themes
In Yume Nikki, it is common for NPCs or backgrounds to resemble body parts or inner organs. See also Themes of Anxiety above for a description of hands in this game. Other examples are the Body Parts in Eyeball World, but also the uteri-shaped creatures on the Endless Road.
Some fans suggest furthermore that KyuuKyuu-kun, a large colorful worm-like creature who is seen rubbing the handrail of a stairway, is phallic imagery, as to access them Madotsuki has to go through a zipper in the wall. For whatever reason, Madotsuki seems concerned or engaged with body related things with how frequently they appear in her dreams.
Another prominent body related theme found is various strabismic NPCs (strabismus meaning to be unable or having problems with fixating both eyes on one point at the same time, leading to the eyes not being aligned).
The most well known strabismic character of Yume Nikki is Seccom Masada-sensei, but other characters such as KyuuKyuu-kun are shown with strabismic eyes as well.
A few fans suggest Madotsuki herself would be shown to be strabismic if she would open her closed eyes.
Themes of Violence
Depending on the player's actions, Madotsuki can behave violently towards NPCs and sometimes inanimate objects. She is able to use the Knife Effect on almost all of the NPCs with varying results.
While this makes the Knife a prominent effect in the game, it is nevertheless unnecessary for gathering effects and thus archiving The Ending, and most of the time can be replaced by the Cat Effect for exploring purposes. Still, the Knife stuck in the minds of fans, leading to many imagining Madotsuki or other characters from this game as characters prone to violence.
Themes of traffic accidents
Different areas in Yume Nikki imply that Madotsuki often thinks about traffic accidents of some kind. Examples of this are Shitai-san, a dead person on the ground on the round Dense Woods surrounded by traffic cones, of whom the Stoplight can be gained. Seccom Masada-sensei is troubled by his spaceship crashing onto Mars, while Mars-san cries near something that appears to be a crashed locomotive. In Dense Woods, Madotsuki can also board a Traincar, taking her to the Witch's Island where a creature similar to Mars-san can be found.
Aztec imagery
Aztec imagery appears in most backgrounds in Madotsuki's dreams and even her real life room (the carpet). It could indicate that she has a strong interest towards Aztec culture and history.
Lucid Dreaming
As Madotsuki can wake herself up at any time in her dream and has control over her surroundings, she is by definition dreaming lucid dreams. Since she also keeps a dream diary, she remembers at least some things about them. Self-induced lucid dreaming is a successful therapy technique for dealing with sleep cycle affecting mental disorders or illnesses.
She may have been taught self-induced lucid dreaming to reduce frequency of nightmares and keeps a dream diary to keep track of her dreams as a self-care exercise.
Seperation of Dream and Reality
At all times during regular gameplay, and unlike some fangames that followed Yume Nikki, the dream world and the real world is kept seperate. Meaning, no "unreal" dream elements are carried over during the awake moments. During the Witch's Flight Event Madotsuki even falls out of her bed in the real world to indicate that she moved around in her sleep while having a strong dream.
However, after The Ending, two Jellyfish appear, while the ending supposedly takes place in the real world. This has raised doubts in fan's minds of The Ending being real and not another dream. In fact, some fans believe that Madotsuki is dreaming at every point in the game, citing her perpetually closed eyes and the unrealistic nature of living in an apartment without food or a bathroom as evidence.
Theories regarding locations
Hospital themes
The location dubbed The Mall by fans has several rooms that closely resemble a doctor's or therapy's office, complete with a reception, fitting wall posters, two couches and a a character sneezing. Entering a second room from the room with the reception leads you to O-Man, a character playing cheerful music. As the Flute can be found here, Madotsuki is able to perform music together with O-Man. This suggests the Flute Effect is given to you by O-Man themself. Tying into the hospital theme, this may be a reference to music therapy.
In another room that is similarly structured to the above rooms, there is a character who has a large amount of red liquid coming out of its head and falls over when interacted with, spilling said liquid on the floor. Beating heart sound effects accompany this, adding to the hospital theme.
The Pink Sea as a party
The dominating cheerful pink and pastel colours, the floating balloons and the conical structures that resemble Japanese-style party poppers in The Pink Sea may represent a party. And as Poniko is the only inhabitant of The Pink Sea, it might be thrown for or by her.