Rebecca Yarros' Empyrean series follows Violet Sorrengail as she enters a brutal war college that trains dragon riders. The first book, Fourth Wing, went viral on BookTok (TikTok's book community) in 2023 and became one of the best-selling books of the year. The third book, Onyx Storm, released in January 2025. Five books are planned total.
Fourth Wing is classified as New Adult, a category intended for readers 18-25. The distinction between New Adult and Young Adult matters: New Adult fiction includes explicit sexual content and more graphic violence than traditional YA. And because BookTok's recommendation algorithms don't filter by age appropriateness, Fourth Wing gets recommended to teenagers alongside actual YA titles like Percy Jackson and The Hunger Games.
That's exactly the kind of situation Shelf Checkout is built to help with. Below is a factual breakdown of content across the three published books in the series.
The Bottom Line First
Book 1: Fourth Wing (2023)
Violet Sorrengail was supposed to enter the Scribe Quadrant, studying history and languages. Instead, her mother, a commanding general, forces her into the Riders Quadrant at Basgiath War College, where students bond with dragons or die trying. The mortality rate is not a figure of speech. Cadets are killed in training.
Violence: Significant and integral to the plot. The war college actively weeds out cadets through physical combat, and deaths are frequent. Characters fall from heights, are burned by dragons, are stabbed, and have their throats ripped out. Fight sequences are described in graphic detail. Violence serves as a core story mechanic, not an occasional event.
Sexual content: Two extended, explicitly described sex scenes occur late in the book (around chapters 30 and 32). The romance between Violet and Xaden builds throughout the story. Descriptions include nudity and sexual acts. The book is frequently described by readers as "spicy," a term indicating significant sexual content.
Language: Strong profanity throughout, with frequent use of the f-word.
Substance use: Characters occasionally drink alcohol and smoke a substance that produces cannabis-like effects. These scenes are incidental rather than central to the plot.
Themes: The story explores chronic illness and disability (Violet has a condition affecting her joints and mobility), loyalty, betrayal, war ethics, and the tension between family duty and personal choice.
Bottom line: Despite sometimes being shelved near YA, Fourth Wing is a New Adult novel with explicit sexual content and graphic violence. The protagonist is 20. The content is meaningfully different from YA fantasy like Percy Jackson or even The Hunger Games.
Book 2: Iron Flame (2023)
Iron Flame picks up directly after Fourth Wing's cliffhanger ending. The conflict broadens beyond Basgiath as Violet discovers that everything she's been taught about the war is a lie. The stakes escalate, the world expands, and the content intensifies.
Violence: Continues at a similar intensity to Book 1, with an added emphasis on torture as a significant plot point. Combat sequences remain graphic. The stakes escalate as the conflict broadens beyond the war college.
Sexual content: Multiple sexual encounters, continuing the explicit tone established in Book 1. The physical relationship between Violet and Xaden deepens. The sexual content is comparable in explicitness to the first book but more frequent.
Language: Consistent with Book 1. Strong profanity remains frequent throughout.
Themes: Expands on themes of political deception, the cost of war, trust, and the complexity of choosing sides when both have legitimate claims. The scope of the world and its conflicts grows significantly.
Bottom line: Iron Flame escalates in both violence (torture is a significant element) and the frequency of sexual content. Parents who found Book 1 borderline should be aware that Book 2 does not pull back.
Book 3: Onyx Storm (2025)
The third installment continues the overarching conflict as the war reaches new stages. The personal and political stakes are higher than ever.
Violence: Continues the pattern of graphic combat and high-stakes conflict established in the first two books. War sequences intensify as the overarching conflict reaches new stages.
Sexual content: Continues in the same vein as the previous books. Explicit scenes are present.
Language: Consistent with the rest of the series.
Themes: Deepens the political and interpersonal conflicts. Themes of sacrifice, moral compromise, and the personal toll of prolonged war come to the foreground.
Bottom line: The series maintains its New Adult content level throughout. Each book assumes you've accepted the content intensity of the one before it.
The BookTok Factor
It's worth understanding how most teens discover this series. Fourth Wing went viral on BookTok, where it's recommended alongside other romantasy titles (a genre blending romance and fantasy). The social media buzz rarely includes content specifics. Your teen may be asking for it because every reader they follow online is talking about it.
That doesn't make it good or bad for your kid. It means you may want to know what's actually in it before the book arrives.
The same pattern plays out with other BookTok favorites. A Court of Thorns and Roses (ACOTAR) by Sarah J. Maas follows the same trajectory: shelved near YA, recommended to teens, explicit content inside. If your teen is asking for Fourth Wing, they may also be discovering ACOTAR and other New Adult series through the same channels.
How Shelf Checkout Helps
When you scan any Empyrean series book with Shelf Checkout, you get a detailed content breakdown across 25 categories, not just the broad strokes above. The app lets you set your own filters based on what matters to your family, and gives you a personalized verdict for each reader in your household.
Every family draws lines in different places. Some parents are comfortable with graphic violence but want to know about sexual content first. Others focus on language or substance use. Shelf Checkout gives you the specific information you need to make the call that's right for your family.
See how parents are using it and check whether a specific book is appropriate for your family.
Related: ACOTAR Parents Guide · Hunger Games Parents Guide · Percy Jackson Parents Guide · Wings of Fire Parents Guide · Do Books Have Age Ratings?