YMMV / The Testament of Sister New Devil

• Complete Monster:
  • Zolgia is the first major villain encountered by Basara Tojo and his friends. A hedonistic Demon Marquis who helped overthrow Mio's father, Demon Lord Willbyr, Zolgia desires to restart a war to show how amazing he is on the battlefield, and also murdered Mio's foster parents, a pair of kind demon orphanage owners. Zolgia regularly abducts other attractive young men and women to rape, relishing in the pain from breaking their pacts to other masters and servants while having them and others' minds broken to serve as doll-like playthings for his amusement. Zolgia's loyal creation Zest fares no better, as Zolgia plans to rape her and dispose of her when she ceases to be of use before replacing her with an identical clone to repeat the cycle.
  • Belphegor, head of the demon council, is known as a war hero to the demon realm but is in truth a monstrous killer who masterminded Lord Willbyr's fall using Lord Leohart as a proxy. Having murdered Leohart's foster parents, he threatens the life of Leohart's adoptive sister and lover Liala to force his compliance. Having helped to create the demon god Chaos, Belphegor plans to have his servants commit genocide on the demonic moderates while unleashing Chaos to kill the rest to shore up his own power. A Serial Rapist as well, Belphegor frequently has women brought to him while violating them body and soul, draining their life force until they are broken shells to keep around or until they simply die at which point he simply orders more brought to him.
• Ensemble Dark Horse:
  • Despite being somewhat of a minor character compared to the other girls, the Older Nurse Chisato is a favorite among the fandom.
  • Yahiro/Lars is also a fairly popular character for his frenemy relationship with Basara and his Big Damn Heroes moment in Volume 3. Being voiced by Tomokazu Sugita and Ray Chase doesn't hurt, either.
• Jerkass Woobie: Takashi, we're sorry that your mother was killed in the Brynhilder/Banishing Shift incident, but Mio watched her foster parents getting killed in front of her and you don't see her acting like a bitch! And don't even get started with Basara's perspective!
• Moral Event Horizon:
  • If Zolgia didn't cross it when he killed Mio's foster parents, he most certainly did when he tried to kill Zest once she was of no use to him and went even further by brutally killing Maria's mother, Shella, whom he later found out had been switched with a doppelganger by Lars.
  • Belphegor crossed it big-time when he killed Leohart's foster parents.
• Paranoia Fuel: Basara and Mio are under constant mundane and magical surveillance. Numerous characters hit him in the face with knowledge about acts that are supposed to be private or behind magical barriers. Lars makes him aware about the fact that Zest saw him use Banishing shift in the duel with Yuki, Kurumi, and Takashi. Zest showed Zolgia a video recording of the same, and his "intimate" moments with his harem. Chisato used her knowledge of the antics in the Tōjō household to blackmail him into a bit of Sexual Extortion, and Ornis responded to that by manipulating a large group of innocent humans to attack him on a train platform on his way home, and then again at school.
• Squick: The fact that Basara has ongoing sexual relationships with both his biological aunt and his cousin.
  • The OVAs only have Basara and Chisato go as far as makeout sessions and foreplay. In the light novels, it's revealed that Chisato's hidden desire is to be dominated by him and finally gives him her virginity near the end of volume 7. The final volume has Basara spend an entire "year's" time repeatedly having sex with her inside a space-time barrier, until he succeeds in bending her completely to his will.
  • Mio begins to participate in orgies with Basara and the rest of his harem by volumes 10 and 11. By the time the series ends, she's among the 8 girls wed to him and they're all pregnant. Chisato casts a protective barrier around each embryo, which allows Mio and the others to continue to have sex with Basara, without risk of miscarriage.
• Stoic Woobie: Poor Basara. He doesn't show much emotion when dealing with demons who attack his stepsisters or former comrades who frequently call him on his actions, but Mio is at least aware that it does bother him lots.
• Unintentionally Unsympathetic: The hero clan, especially Takashi, resenting Basara is meant to come off as a Jerkass Has a Point since their friends were inadvertently killed by his Banishing Shift. However, most fans ignore it due to the fact that they were Basara's friends too, his Banishing Shift was triggered by the demon hunter's Brynhildr-induced rampage that he himself caused and if it hadn't, Basara and Yuki would very likely have been two more casualties before he likely would've gone on to slaughter the rest of the village unopposed, and they come off less as knights in shining armor tasked with protecting humanity and more as self-righteous psychopathic hypocrites who go out of their way to try and murder an innocent girl just for petty revenge. Their actions don't sit well with Mio at all. To compound their hypocrisy, we have Nanao's testimony as to how her home village was wiped out for the Crime of Self-Defense, and her people brought to the brink of extinction... Then Basara returns from the Demon World, which he was dragged to, after eliminating a major threat in the form of Chaos (a Class 3a threat minimum), and how do the village elders react? Summoning him back to the village for violating taboos that no longer apply to him, as he's an exile. It seems they conveniently forgot that Basara's actions should have benefited the truce that was made between the Hero Clan and the Demon Factions but they took the side of the person who nearly damned them in the first place and failed to learn from that mistake.
• The Woobie: Mio's father was murdered, the people who she thought were her parents died protecting her, and she is constantly pursued by demons who want to steal her power and Heroes who view her as a threat and try to murder her on sight. All she really wants is to live like a normal human girl.