The Testament of Sister New Devil Review: A Demon Lord's Daughter and Her Succubus Companion Become a Boy's Stepsisters
by Tetsuto Uesu / Fumihiro Kiso
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Quick Take
- The hero vs. demon setup quickly gives way to a harem fantasy driven by the master/servant contract's M-rated implications — the action is genuine but secondary to the fan service
- The character interactions are warmer than the premise suggests, and Basara's protectiveness is consistent
- 12 volumes complete; significant M-rated content with genuine supernatural action
Who Is This Manga For?
- Adult readers who want supernatural harem action with M-rated content
- Anyone interested in the hero/demon dynamic inverted through family structure
- Fans of master/servant contract romance in action context
- Readers who accept heavy M-rated content with genuine action elements
Content Warnings & Age Rating
Age Rating: M (Mature) Content Warnings: Explicit fan service and mature sexual content throughout; master/servant dynamic with explicit implications; supernatural violence; harem elements
M rating — adult readers only; content is prominent throughout.
Yu's Rating
| Category | Score |
|---|---|
| Story Depth | ★★★☆☆ |
| Art Style | ★★★★☆ |
| Character Development | ★★★☆☆ |
| Accessibility for Non-Japanese Readers | ★★★★☆ |
| Reread Value | ★★★☆☆ |
Story Overview
Basara Toujou belongs to the Hero Clan — people who fight demons. His father announces a new marriage and introduces two stepsisters: Mio Naruse, daughter of the previous Demon Lord, and Maria Naruse, a succubus serving her.
This is a situation the Hero Clan would ordinarily resolve through combat. Basara's response is different — he forms a master/servant contract with Mio instead, placing himself as her protector against both demons who want to use her as the new Demon Lord and Heroes who see her as a threat.
The master/servant contract has specific implications in the series' magic system that generate the M-rated content. Alongside this, Basara's genuine protectiveness and the developing found-family dynamic provide the series' warmer elements.
Characters
Basara Toujou — A protagonist whose protective instinct is genuine rather than possessive; his willingness to cross factional lines for people he cares about is the series' heroic core.
Mio Naruse — The demon lord's daughter whose inherited power and uncertain position in both demon and human worlds create her specific vulnerability.
Maria — The succubus whose magical abilities and personality provide the series' comedic energy.
Art Style
Kiso's art handles both the M-rated content (explicitly) and the supernatural action (with genuine energy). The demon designs are visually varied and the battle sequences have real impact.
Cultural Context
The Testament of Sister New Devil is adapted from a light novel series. The setup — hero and demon forced into family structure — inverts the typical Hero/Demon Lord conflict by making the personal override the factional. The series uses the master/servant contract as a mechanism for the M-rated content while maintaining the supernatural action plot as a parallel track.
What I Love About It
Basara's factional refusal. He belongs to the Hero Clan. Mio is the daughter of a Demon Lord. The appropriate action is clear, and he refuses it because the appropriate action would harm someone he has decided to protect. The series' best moments are when his choice creates consequences with the Hero Clan.
What English-Speaking Fans Say
Western readers describe The Testament of Sister New Devil as a solid M-rated action romance that is more interesting than its premise suggests — specifically noted for Basara's protective motivation being genuine rather than possessive, for the supernatural action being a real plot rather than M-rated cover, and for the found-family elements creating warmth alongside the fan service. Content level is consistently noted as significant.
Memorable Scene ⚠️ Spoiler Warning
The scenes where Basara's choice to protect Mio creates direct conflict with the Hero Clan — and he holds his position despite the institutional pressure — are the series' most character-defining moments.
Similar Manga
- High School DxD — Supernatural harem action with similar content and structure
- Rosario+Vampire — Supernatural school romance in lighter register
- Yuuna and the Haunted Hot Springs — M-rated supernatural harem in different setting
- Servamp — Supernatural contract dynamics in less explicit register
Reading Order / Where to Start
Volume 1 — The family formation, the revelation of identities, and the contract establish the premise.
Official English Translation Status
Yen Press published the complete English series. All 12 volumes available.
Pros & Cons
Pros
- Basara's protectiveness is consistent and genuine
- Supernatural action is a real plot element
- Found-family warmth alongside fan service
- Complete in 12 volumes
Cons
- M-rated content is very prominent
- Master/servant dynamic may not suit all readers
- Light novel adaptation means some compression
Format Comparison
| Format | Notes |
|---|---|
| Individual Volumes | Yen Press; complete series |
| Digital | Available |
Where to Buy
Get The Testament of Sister New Devil Vol. 1 on Amazon →
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Written by
Yu
Manga Enthusiast from Japan
I grew up in Japan and manga literally saved me during a tough time in elementary school. My English isn't perfect, but my love for manga is real — and I want to share it with you.
Disclosure: This post contains affiliate links. As an Amazon Associate, I earn from qualifying purchases at no extra cost to you.