“The Testament of Sister New Devil” is a show about a high school boy who accidentally becomes the master of a Demon Lord princess, and then spends the next twenty-two episodes trying to protect her while getting into one messy situation after another. It is not subtle, it does not pretend to be, and it knows exactly what it is doing. The result is a surprisingly tight, if deliberately silly, adaptation of the light novel series that manages to make its central premise work even when it could have collapsed under its own weight.
A high school student named Toujou Basara finds himself alone when his father remarries and abandons him with two beautiful step-sisters. What he does not realize is that those sisters are actually the Demon Lord and a succubus. After his father departs overseas, Basara accidentally ends up forming a reverse contract with Mio Naruse, making her his master. The show then watches Basara slip into one ecchi situation after another while attempting to protect Mio from demons and heroes who seek her out due to her heritage, which comes from the former Demon Lord Wilbert.
Trailer, via Crunchyroll Store Australia.
Mio, Maria and the Reverse Contract
The core of “The Testament of Sister New Devil” is its contract system. When Mio attempts to make a master and servant contract with Basara, it ends up the other way around. She becomes his servant, and he becomes her master. This inversion is the engine of the entire series, driving nearly every plot point and every awkward encounter that follows.
Mio Naruse is the Demon princess, voiced by Ayaka Asai. She is the one who forces the contract, and her casting is deliberate; she is supposed to be a strong, capable figure who is also deeply attractive. Maria Naruse, voiced by Kaori Fukuhara, is the succubus, and her role is to complicate the situation by being Basara’s other step-sister and by having a different idea about what the contract means. The show uses the two sisters to create friction, with Maria’s antics often pushing Basara and Mio into the kind of close situations the show’s title promises.
Hijirigasaka Academy and the Hero Clan
Basara attends Hijirigasaka Academy, and his family’s claim ties him to the hero clan, which means Mio’s master is awkward from the start. The show spends little time on the hero clan as an organization, but it keeps the threat of other demons and heroes coming after Mio’s legacy shadows the story. That thread gives the series a sense of danger, even if the plot never fully delivers on it, and it keeps the audience engaged.
The school setting is barely more than a backdrop. The story focuses far more on the bond between Basara, Mio, and Maria than on their place of learning. The academy serves only to give the characters a shared space, and it never grows into a driving force of the narrative. This is a story about three people living together, not about a school full of students.
The Voice Cast
The show’s voice cast is the main reason it works. Basara is voiced by Yuichi Nakamura, Mio by Ayaka Asai, and Maria by Kaori Fukuhara. Yahiro Takigawa’s voice is Tomokazu Sugita, while Yuu Asakawa plays Chisato Hasegawa. Iori Nomizu voices Kurumi Nonaka, and Sarah Emi Bridcutt voices Yuki Nonaka. Keiji Fujiwara voices Jin Tojo, and Seiko Yoshida voices Zest.
The voice selections are purposeful. Mio’s voice comes across as that of a princess, Maria’s voice sounds like that of a succubus, and Basara’s voice makes him sound like a high school boy who is completely out of his depth. The show relies on the voice work to sell the absurd situations it puts the characters in, and the cast delivers.
The Ecchi Situations
“The Testament of Sister New Devil” is a comedy about a boy who is constantly put into situations where he is too close to his master. This is the show’s draw, and it is also its limit. The series knows exactly what it is, and it does not try to be anything else. Every episode moves toward a situation where Basara and Mio are in a room together, alone, and something happens.
The program makes no attempt to conceal its intentions, and it offers no excuses for its approach. That forthrightness contributes to its appeal.
The Threat From Other Demons
The series actually carries weight. Its danger comes from demons and heroes who want Mio’s heritage, which keeps the show grounded despite its lighter elements. This threat never fully materializes, but it remains a persistent presence, a ticking clock that never quite ticks, enough to keep viewers engaged.
The show constantly places Mio in peril, and that peril exists to keep the audience on edge. That edge is then used to set up the show’s ecchi situations. It is a deliberate move that works, though it also puts a ceiling on how far the show can push its material.
The Season Structure
The two seasons of the show aired with the first premiering on January 7, 2015, and the second following on October 9, 2015. The original light novels were written by Tetsuto Uesu and illustrated by Nekosuke Ōkuma. In total, thirteen volumes have been published by Kadokawa Shoten since 2012 as part of their Kadokawa Sneaker Bunko series. A manga version has been running in Kadokawa Shoten’s Shōnen Ace magazine since May 2013, and a second manga adaptation has been serialized in Hakusensha’s Young Animal Arashi magazine since February 2014.
June 22, 2015, saw the release of the first OVA episode; the second OVA episode followed on January 26, 2016, and a third OVA episode came out on March 28, 2018.
The way the series is organized matters because it demonstrates how the show was constructed. The first season lays the groundwork by establishing the contract and the core setup, while the second season delves deeper into these elements. The OVAs, by contrast, stand apart as their own distinct material, frequently concentrating on standalone tales rather than the larger, ongoing storyline.
How It Stacks Up
“The Testament of Sister New Devil” is a show about a boy, a princess, and a succubus. It is silly, it is repetitive, and it is also surprisingly well made. The show knows exactly what it is, and it executes that premise with a confidence that many shows in this genre lack.
The show never wavers from its central premise. It refuses to become a drama, a horror show, or a tale meant to be taken seriously. Instead, it treats itself as a comedy about a boy who becomes the master of a Demon Lord princess, and it carries that premise out with a confidence that many shows in this genre lack.
The Verdict
“The Testament of Sister New Devil” is a show that knows exactly what it is. It is silly, it is repetitive, and it is also surprisingly well made. Its commitment to its own premise is its strength, and its refusal to take itself seriously is its charm. It is not a deep show, and it does not pretend to be, but it is a confident one.
This production sticks to what it sets out to do without attempting to reach beyond its limits.
Key Facts Box
- Title: The Testament of Sister New Devil (2015)
- Network: Tokyo MX
- Seasons: 2
- Episodes: 22
- First aired: 2015-01-07
- Last aired: 2015-12-11
- Genres: Animation, Action & Adventure, Comedy, Sci-Fi & Fantasy
Comparison Table
| Aspect | The Testament of Sister New Devil |
|---|---|
| Main premise | Boy becomes master of Demon Lord princess |
| Setting | High school, Hijirigasaka Academy |
| Threat | Demons and heroes after Mio’s heritage |
| Central relationship | Basara, Mio, Maria |
| Animation studio | No single studio given in source |
| Original material | Light novels by Tetsuto Uesu, illustration by Nekosuke Ōkuma |
This series is not a masterpiece, but it is sure of itself. It understands precisely what it is, and it sticks to that premise with a clarity that many shows in this genre lack. It follows a boy, a princess, and a succubus, and it never apologizes for being that show. The result is a watchable, often funny, and occasionally awkward series that earns its own mark.
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