RE Engine
RE Engine is Capcom's in-house game engine. It powers most of Capcom's modern releases, and it is the engine Onimusha: Way of the Sword is being built on.
Why It Fit
Way of the Sword was greenlit in early 2020, and at that point RE Engine's utilities and general-purpose feature set had expanded enough to support the kind of third-person character-action work Onimusha wanted to do. Producer Akihito Kadowaki has publicly said the team did not hit significant engine-level problems during development.
Context
RE Engine has been used across Capcom's Resident Evil remakes and originals, Monster Hunter Rise and Monster Hunter Wilds, Street Fighter 6, Devil May Cry 5, and other recent titles. Onimusha: Way of the Sword slots in alongside that family of games, sharing the animation, lighting, and rendering tech that has defined Capcom's last several years of output.