Japanese independent game developer Kazuya Okada (who goes by Okazu online) was recently surprised to find out that Clair Obscur: Expedition 33, one of the biggest hits of 2025, uses his open-source KawaiiPhysics plugin.
KawaiiPhysics is a pseudo-physics plugin for Unreal Engine that simulates stylized (as opposed to realistic) physics. It applies to various movements, ranging from the bounce of a character’s hair, to the sway of skirts and other flowy materials. With a lightweight and simple algorithm, the plugin helps developers achieve appealing, anime-inspired physics while bypassing much of the hassle involved in manually fine-tuning secondary physics animations. As you can see in the 2024 demo video below, the KawaiiPhysics engine lives up to its name.
Okazu’s creation has long been the secret sauce of various games developed in Unreal Engine, including major titles like Persona 3 Reload, Stellar Blade and Tekken 8. On the other hand, there haven’t been many prominent instances of commercial projects in the West using KawaiiPhysics. Until Sandfall Interactive’s Clair Obscur: Expedition 33, that is.
Funnily enough, Okazu seems to have only found out recently that the hit RPG uses his creation. In an X post from July 22, he shared a presentation slide from a lecture held by Sandfall Interactive on which his plugin is credited among other third-party software used in Expedition 33. “It looks like Clair Obscur Expedition 33 uses KawaiiPhysics! Thank you so much!!!” Okazu commented. The source of the presentation slide is a CEDEC 2025 lecture titled “Clair Obscur: Expedition 33 – Technical choices and challenges to support a wide scope with a programming team of 4 and Unreal Engine.”
Okazu has a live list of games that have used KawaiiPhysics, but as the plugin is issued under a liberal MIT License (to use the plugin, all you need to do is include its copyright notice somewhere in your game), it is likely impossible for him to keep track of every instance. On the flip side, this seems to lead to very pleasant surprises for the dev.
KawaiiPhysics is Okazu’s personal project, developed during his free time. While the plugin is available completely free of charge on GitHub, Okazu recently launched a paid version on Fab for users who’d like to support him financially. There are no differences between the two versions, and Okazu has no plans to make KawaiiPhysics a paid-only plugin in the future. The developer is also accepting support for his work on the plugin via Github Sponsors.
