The Empyrean series had a big new release with Onyx Storm earlier this year and now all three of the books are topping Amazon's Kindle best sellers list for 2025. The popularity of these books really kicked when Fourth Wing was first published in 2023 largely thanks to Booktok. Since then, this romantasy series has grown big enough to top most best seller charts.The fact that the release of Onyx Storm has brought so many new readers to the series is a testament to the viral nature of Rebecca Yarros' writing. It has just the right mix of fantasy and romance to entrance such a broad spectrum of readers. Now that a Fourth Wing TV series has been greenlit at Amazon, the Empyrean series has the chance to become more popular than even the Harry Potter book franchise if it plays its cards right.The Physical Editions Are Popular TooOnyx Storm (Deluxe Limited Edition)The Empyrean series dominates the Kindle charts, but it also sits in Amazon's top selling physical books list for 2025. Both the deluxe edition of Onyx Storm and the standard edition are in the top 10 and Fourth Wing remains in the top 25. Only now that Suzanne Collins' new Hunger Games book has officially been released has Onyx Storm dropped to the second biggest fiction book on the list. Though with seemingly more people just getting into the series with Fourth Wing, we could see that change again before the end of 2025.Fourth Wing and Iron Flame are Part of Kindle UnlimitedKindle UnlimitedSee subscription options.See it at AmazonThe first two books in the Empyrean series are currently free on the Kindle app if you have a Kindle Unlimited subscription. If you want to get into the series, you can log on to your Kindle account and download both Fourth Wing and Iron Flame before they are no longer available with your subscription.Jacob Kienlen is a Senior SEO Strategist and Writer for IGN. Born and raised in Portland, Oregon, he has considered the Northwest his home for his entire life. With a bachelor's degree in communication and over 7 years of professional writing experience, his expertise is spread across a variety of different topics -- from TV series to indie games and popular book series.