Shuhei Akutagawa developed the Phantom CLI tool for the Homebrew/homebrew-core repository, focusing on improving parallel development workflows with Git worktrees. Over the course of a month, Shuhei designed and implemented Phantom to streamline multi-branch development, enabling developers to install and test worktree-based environments efficiently. The project involved Ruby-based Homebrew formula packaging, CLI development, and integration with Git, ensuring reproducibility and ease of distribution through Homebrew. By releasing Phantom 3.2.0, Shuhei addressed the need for faster feature delivery and enhanced testability in modern development environments, demonstrating depth in workflow automation, release management, and developer tooling within the Ruby ecosystem.