- Audience-Alienating Premise: A horror story in which a young girl quite literally devours her older brother in pseudo-sexual fashion is a surefire way of turning off potential viewers.
- Big-Lipped Alligator Moment: The final episode of the anime is full of these, as well as the last Story Arc of the manga.
- Bile Fascination: One of the main reasons viewers watched the anime adaptation. Many go check it out after hearing how it's "one of the ugliest anime ever made". For the most part, they are right.
- Broken Base:
- In-universe, Yume is this. Utsutsu sees her as his adorable little sister and his Living Emotional Crutch. Everyone else, especially Shiro and Sachiko, see her as a Creepy Child and unrepentant Eldritch Abomination. And judging their flashbacks, they might be right.
- Just how justified Shiro was in his actions remains a topic of debate, particularly given that he's portrayed in the anime as an unrepentant abusive dad. The manga portrays him as a Jerk with a Heart of Gold who cares about Utsutsu, but he's deluded into thinking love is violence. While the burnmarks were his doing, the scar in Utsutsu's eye wasn't his fault. His abuse towards Sachiko and Yume is justified: he knew Yume wasn't his child, but since at the time he didn't know about the Pupa virus, he believed that Sachiko betrayed him. Not to mention that he has a Freudian Excuse for his violent behaviour.
- Utsutsu is either a Knight Templar Big Brother and a great deconstruction of the Iron Woobie, or a pile of Wangst who's nuts for no good reason and refuses to see that Yume is a creepy Eldritch Abomination (on his defense, he never saw that because Yume was only nice towards him and humanized as the years passed). His relationship with her was either one of the best-explored romantic relationships or really, really creepy (though few would call it a very healthy one).
- Not to mention that Utsutsu's creepy overprotectiveness towards Yume (especially after we found more details about her) and his denial of Yume's being an ancient monster, is either an endearing staple of the series, or people find it disturbing, and too annoyingly in-your-face, to take seriously.
- Complete Monster: Genjurou Imari is the posthumous grandfather of Maria "Ai" Imari. Founding the Imari Ishin Facility alongside Bizen Chiharu, Genjurou believed that suffering was the truest art form. Adopting orphans and taking them back to his island, Genjurou would torture them by whipping them severely, making them muses to serve as inspirations for his paintings. Genjurou adopts Shiro Onijima and subjects him to years of horrific torture, as well as psychologically warping his mind into accepting the abuse as "loving". While he may not have shared his granddaughter's aspirations, Genjurou is a depraved pedophile who entertains himself with torturing his victims to his heart's content.
- Darkness-Induced Audience Apathy: The very fact that Yume was an Eldritch Abomination all along, instead of being infected (as viewers first thought) caused many viewers to be turned off by the series. It also doesn't help to note that a lot of the human and monster characters (except for Yuu) have very unlikable personalities that makes the audience hard to relate with (especially Yume, Utsutsu, Maria and Shiro).
- Ho Yay:
- Yuu gets really touchy-feely with Utsutsu and gives him barely any personal space. That might be more because of Yuu's lack of common sense. Also, basically Yuu is like a male Yume, naive about the world and Adorkable in general. Of course, Utsutsu being Utsutsu, finds Yuu's quirks annoying and disgusting, but finds Yume's adorable.
- Shiro's partners in work, Haruka and Ryuichi, not only know about Shiro's sadistic tendencies, they love him for it!
- It Was His Sled: Yume was a monster all along.
- Iron Woobie:
- Utsutsu has an estranged family, his sister is turned into a flesh-eating moster that can only satisfy on his flesh, he is slowly going insane, and is attacked by supernatural forces who would love to dissect him and his sister many times during the series yet still keeps trying to save his sister. And it turns out that most of what he believed about his family were lies and actually his real family problems were caused indirectly by Yume.
- Yuu. He was separated from his mate by human scientists. Yuu kept waiting for her until he found out that his mate is incarnated as Yume Hasegawa and has forgotten about him. When they finally met, she rejects him, choosing Utsutsu over him. After angsting for a while, he pulls a I Want My Beloved to Be Happy. And then, she dissintegrates into butterflies with Utsutsu.
- Jerkass Woobie: Shiro in spades, once his backstory is revealed. He was abused by a Mad Artist when he was just a child, who was fond of stripping him naked and whipping him to get inspiration for his paintings. Said artist convinced Shiro that violence was the purest form of love. After his captor died, Shiro found difficult to live a normal life and choose to work for an organization, where he could put his newfound sadism into use. Then, he gets his friend Sachiko pregnant and marries her, but he has to leave for five years due to work. After he returns, turns out Sachiko has a second child (Yume), so he believes she cheated on him. He became abusive towards Sachiko and his son Utsutsu, thought it's implied that Genjurou's abuse warped his view of affection. Then, his wife Sachiko is driven mad due to Yume. So he takes his frustrations on Utsutsu. When he finds out that Yume is an Eldritch Abomination, he tries to warn Utsutsu and beats him again. Then Utsutsu is revealed to be a monster (infected by Yume as a child) and dissolves into butterflies. Sucks being him.
- Narm: The ending should be a complete Tear Jerker, what with Utsutsu and Yume dissolving into red butterflies, and the only thing that remained of them was their hairpins... As their voices resounded in the far-off distance... "YUME.... ONII-CHAN.... YUME.... ONII-CHAN."
- Tear Jerker: Now has its own page.
- They Wasted a Perfectly Good Plot: For some, the fact that the anime is so short and poorly animated and spends most of its time with little or no continuity is a point of frustration, the ending was cut short as well.
YMMV / Pupa