The Vast One is a Metroidvania-style action-adventure game where players control Rusty, a decomposer robot, on a mission to restore a devastated Spirit Tree ecosystem. After a catastrophic event, Rusty must explore interconnected regions, each guarded by a unique robot, solving environmental puzzles, collecting resources, and reviving inactive machines to unravel the game's narrative. This project focuses on developing the game’s initial area and prototype, culminating in the revival of Zephyr, the guardian of Hollow Vents, the first region. The design process involved market research, narrative development, level design, and iterative prototyping in Unreal Engine 5. Inspired by Ori and the Blind Forest, Hollow Knight, and Prince of Persia: The Lost Crown, the game emphasizes fluid exploration, intricate level design, and immersive environmental storytelling. Featuring a Studio Ghibli-inspired art style, the game transforms hand-drawn aesthetics into a post-apocalyptic 3D world, merging nature and technology into a visually captivating experience.