Yumeji Fujiwara has a strange ability. He can see the aura of peoples' dreams. Around himself, there is a black aura. A nightmare. Though Yumeji lives a comfortable life with his childhood friend Isana and his school's Literature Club, he's had a recurring dream of cats. Multiple cats attacking him, trying to claim his body so they can cross over from the nightmare to our world.There is another party involved. A girl in a strange set of clothes. She falls on top of Yumeji one day and, after getting her hat back, finds her way into his world. Her name is Merry Nightmare, a dream eater. She has no memories of where or who she was, and seeks to return to the world of dreams.Based on a manga by Yoshitake Ushiki, Yumekui Merry was adapted into an anime in the winter of 2011 by JC Staff. Touhou fans may recognize the author from his doujinshi work Advent Cirno, and the people handling the music as IOSYS.Now has a Character Sheet, which Needs Wiki Magic Love.
Tropes in Yumekui Merry include:
The Ace: Shiragi Kyou transfers in to their school and is a dedicated perfectionist, talented at everything he puts his hand to.
Bare Your Midriff: Merry. The animators seem to be actively trying to put in as many shots of Merry's bellybutton as they can.
Bathtub Bonding: Isana and Merry get to know each other in the bath when Yumeji walks in. Isana notes this is the fifteenth time he's done that. Later, John and Yumeji get in on this, only for Merry to walk in on him.
Beta Couple: Takateru and Saki look like they're shaping up to be this (with the Alpha Couple being Yumeji's harem).
Subverted with Takateru, whose eyes are almost entirely black (with very thin slices of whites visible around them), only he's probably the nicest guy in the cast. Played with. See, he's possessed by the Big Bad... but Taka really is that nice, normally.
Break the Cutie: See below. Also what happens to kids after the dream demons are killed.
Cat Girl: Chaser John Doe has some working for him.
He later brings a whole army of them to help Merry and Yumeji. They can transform into cats, sans-clothing, in order to escape from being hurt then transform back again with clothing starting to form itself around them. Yes, they are made of fanservice, why do you ask?
Clingy Jealous Girl: To an extent, Isana. She's not really all that clingy, but she DOES get jealous when a girl she doesn't know shows up asking for Fujiwara. It's Yui (and Engi) coming to train him and Merry. All considering, her jealousy may just be for Rule of Funny.
Taka's little sister for her "onii-chan".
Clothing Damage: A non-fanservice type happens during Merry's fight with a Dream Demon in the 6th volume. Her opponent thinks that her coattails look like eels and he rips one of them off. Merry isn't amused.
Other non-fanservice example is Yumeji, from Chapters 57 to 60, his ripped and bloodied shirt looks a lot like a dark version of Merry's"tails".
Cloud Cuckoo Lander: Yui, with her penchant for concocting strange stories about the dolls she collects.
Color-Coded for Your Convenience: Yumeji can see what kind of dreams people will have from the color of their auras. Often he's wrong, since most dreams are a confusing array of colors rather than anything stable and coherent, except for...
Black: Is 100% nightmares and daydreams when a Dream Demon tries to take over a host.
Mr. Ijima, Yumeji's teacher in the anime, could be seen as this as well. Sure he has an extreme liking of rice, but his speeches to his students are quite inspirational. Of course, it's all a ruse, but...
Cute Bruiser: Merry. Chaser John Doe notes how much strength Merry can invest in those flimsy little arms. In the waking world she's not quite as strong, but she's still pretty sturdy for her slender little frame.
Dull Eyes of Unhappiness: The victims of Dream Loss Syndrome, who are not so much unhappy as unmotivated, almost to the point of complete catatonia. They were formerly symbiotes or possessed vessels of Dream Demons; when the demon's killed, all the dreams and ambitions of the human vessel die with it.
Exotic Eye Designs: Most Dream Demons have unique-looking pupils. For example, Chukai has cross-shaped pupils, while Chris Evergreen has tilting H-shaped pupils.
Expressive Mask: Chaser John Doe. It's very subtle, but his otherwise motionless mask can change from a frown to a smile or vice versa between shots.
Finger Gun: Chizuru does this a few times, saying "bang" as she does it.
Genius Loci/Eldritch Location: Each nightmare is not only the discrete person, but their "yard" or the field that forms around them in a daydream. So John Doe is as much the empty city that he chases Yumeji through at the very beginning, and the cat warriors who fight for him, as he is the masked cat-man who does the chasing. Hercules's greatest power, as the "lighthouse", is to direct others into his own yard where he controls the shape of local reality, which means he has the home field advantage whenever he wants it.
Merry has one on her right arm, she just keeps it covered until the Beach Episode in chapter 11. Yumeji had a scar, but it's long since faded. Curiously, his was in the same place that Merry's is. And now the spot where he had his scar is starting to hurt after he exits a daydream...
This page shows some of the eye patterns that were seen in the manga. Clockwise from the the bottom-left: Chain Noir's looks like a chain-link, Engi Threepiece's is a triangle, Ichima's is a swirl, Chaser John Doe's is his mouth on his mask, Chris Evergreen looks like a sideways H, Maze Landsborough's looks like a sideways #, and Pharos Hercules looks like a sun or a shining light.
In chapter 24, Yumeji's eyes took on the pattern of John's mouth on his mask when he first formed John's weapon. In Chapter 25, Yumeji's eyes took on the pattern of Ichima's swirly eye pattern when he used her power to call forth one of her giant toys to protect John. In Chapter 30, Yumeji's right eye takes on Chris's eye pattern when Yumeji uses Chris' Rocket Punch move.
Hidden Agenda Villain: Pharos Hercules draws nightmares to the waking world, brutally kills any that won't follow him, and lets his followers run wild. John Doe is trying to puzzle out his plans, questioning every revelation, even those from Hercules's right hand minions. Merry thinks Hercules is just out to cause chaos and is using the appearance of a master plan as cover to keep his foes guessing. Hercules eventually reveals his grand scheme: to destroy the Gate between Dream and Reality so nightmares may be physically present in the real world, but not so he may conquer the world - but so he may crush and destroy everyone, nightmares and humans both. He is a nightmare of fire after all, the signaling flame, and as a living fire all he wants is to consume and burn brighter. So technically Merry was right, but his methods were frightfully sophisticated.
Improbable Weapon User: Chaser John Doe has something that the author said was a cross between a saw and a guillotine. Yumeji, using his Lucid Gadget, creates a smaller version to use against Chain Noir.
Lethal Chef: Yui. Her teacher calls her brand of cooking Magical Chemical Cooking. Yui's friend Nao has also said that not even a dog would eat Yui's cooking.
Light Is Not Good: Heracles is described as the guiding light (the kanji of his name make up the word for lighthouse), drawing other Dream Demons to Reality. Because of that, the whole balance between the worlds has been thrown out of whack. Then there's his personality...
Yui Konagi, Engi's vessel. When Yumeji does a diving save for a doll she drops, he saves the doll, but catches a glimpse. The audience also gets a peek in the manga.
Played with in the manga by villain Maze Landsborough. At one point he winds up on the floor between Merry's feet, looking up; we see stripes reflected in his one eye, but not from her stockings. Yoshitake Ushiki's inventiveness and subtlety - establishing what kind of panties the heroine wears WITHOUT a single Panty Shot - is to be admired.
We get another brief one in volume five. Hey, when you've got Stripperific cat girls fighting, you're bound to get at least one.
Meaningful Name: The names of both lead characters are related to dreaming: Yumeji - "Yumeji" means "Dream Road", or "Road to Dreams" depending on personal interpretation. Merry's surname is Nightmare, and her full name is Sheep Merry Nightmare. The author also states in an omake that her name is based on Mary, as in 'Mary Had a Little Lamb'.
Both of the protagonists' names explain themselves. Yumeji could mean "Path to the Dream", which is his Chekhov's Skill, while Merry Nightmare, as ridiculous as it may sound, just mean merry nightmare.
Many of the Dream Demon's names are this, like Chaser John Doe being a hunter, Maze Landsborough traps people in a maze, Chain Noir uses chains, etc.
Pharos means Lighthouse and is referred as the light that guides all the other nightmares to the real world. This becomes even more meaningful when you remember that a lighthouse is to guide, and only to guide.
Mega Manning: Yumeji can call upon the powers of Dream Demons he met before.
Mood Whiplash: At one point, Yumeji is injured and at the mercy of Chaser John Doe, who coldly tells him that it would be incredibly easy to take over his body at that moment. Yumeji cringes at what's coming – but John promptly states that to do so would be crude and unsportsmanlike ("I am a hunter, not a thief"), and summons a pair of cute voluptuous cat girls to tend to Yumeji's wounds!
Also Taka's story about his little sister where he talks about how she was sickly when she was little and kept being bounced from hospital to hospital until she could no longer smile. At least until Taka started with those ridiculous poems of his, sparking his dream of wanting to make everyone he meets laugh through his poems. He then pauses before saying that she's completely healthy now and even working part-time at a burger joint.
And you get another one from Chapter 36, when it is revealed that Takateru is Hercules's host, and his little sister being healthier is due to Hercules putting a dream demon in her, to hold her hostage against Takateru.
Off Model: Several scenes seem rushed and shoddy compared the rest.
Oh Crap: Yumeji gets this when he hears the people in his class talking about how they all had the same nightmare. He uses his dream-seeing trick and...every single person has the same black aura.
Engi gets one after Merry starts going berserk due to Yumeji being nearly cut in half. Especially the moment when Merry shattered all of Engi's swords, prompting Engi to try rallying her nerve while explaining her blade could keep reforming forever as long as there was moonlight, to which Merry simply lifts her hand and shatters the moon. 
Happens in episode nine of the anime when Yumeji learns that Isana's been possessed by a Dream Demon.
Pharos gets one as well. And it's deliciously so, when Yumeji copies his ability.
P.O.V. Boy, Poster Girl: Yumeji is the main protagonist and a decent fighter in his own right, but without Merry, there would be no plot.
Power Degeneration: Any use of a nightmare's power while possessing a person or bodily manifest on Earth causes a kind of backlash against the Gate between worlds. This includes Merry's own strength, and as she is the Gate as well as the Sheep, it means that all her fighting to push nightmares back across the Gate has been harming her. In the battle against Hercules, Merry nearly destroys herself from using too much of her power in a blind rage.
Refuge in Audacity/Did We Just Have Tea with Cthulhu?: Mr. Iijima trolls the entire cast by visiting the STO café; he sits down and orders coffee right in front of the protagonists. By this time they have already found out that he's Treesea's vessel and the one responsible for a lot of literally crushed dreams, and they're also painfully aware that he's scouting his next victim (Isana), but right then and there they can't do anything about it.
Running Gag: Two so far. Yumeji walking into the bath...and someone's already there, usually it's Isana. She notes that he's done this fourteen times before the two that we see in story. Later, Merry walks in on HIM. Also Yui telling people to depend on her as an older sister, and then being told she's younger than they are.
In at least half the glimpses we get of Full Hell Boarder Glitchou, the main character hurts his wrist or ankle. It eventually gets lampshaded by Merry when Yumeji complains about a sore wrist and she asks if he's pretending to be Glitchou.
Stylistic Suck: Yumeji's writing, mostly because he's trying to reflect the bombastic, over-the-top action and acting of Tokusatsu hero shows in written fiction, where it mostly comes off as ridiculous.
Chris Evergreen is existing as a Symbiote to Mei, but he's about to take the next step when Yumeji and Merry intervene.
This is actually the most productive way for Dream Demons and humans to interact. If a Dream Demon tries to take over full time, the host will wake up, possibly at the worst possible moment.
Theme Tune Cameo: During the first karaoke-bar scene in Episode 4. Someone down the hall is heard singing the OP, and doing a remarkably good job of sounding like the original singer.
The Nicknamer: Merry gives nicknames to some of the characters. She calls Engi Threepiece "Eggplant Lady". She calls Chaser John Doe "Cat Mask". She calls Pharos Hercules "Lighthouse Guy". She calls Mistilteinn Treesea "Wood Lady"
There's No Place Like Home: Merry's main motivation. Curiously (it may be a plot point), Merry doesn't have enough of her memory intact to understand why she wants to go back — she only knows that she wants to go back.
Title Drop: In episode three as a nickname for Merry given by Yumeji, comparing her to a baku — a tapir-like beast from Japanese mythology which hunts and eats nightmares. She argues that she does not actually eat them. The fourth episode is also called "Dream Eater Merry".