Agentic AI: Comparative Legal Applicability and Governance in Japan, the European Union, and the United States

Agentic AI systems plan, call tools and execute multi-step tasks with limited human supervision, straining legal frameworks built for static models or human-directed software. This article asks how far existing law in Japan, the European Union and the United States applies to agentic AI, and where governance gaps remain. Using a functional comparative method, it examines five pressure points: classification and scope, human oversight, transparency, attribution of acts and contracts, and liability. Materials are current to 23 October 2026. None of the three jurisdictions regulates agentic AI as a distinct legal category. The EU reaches agents through the AI Act, whose high-risk obligations the 2026 Digital Omnibus deferred, and the revised Product Liability Directive. Japan relies on a promotion-oriented framework statute without dedicated penalties, official guidance, including 2026 guidance on civil liability for AI, and general private law. The United States combines federal policy that does not pursue a horizontal AI framework with sectoral and state law and commercial-law rules on electronic agents. Coverage is strongest for systems, models and deployment contexts, and weakest where an agent acts under delegated authority. Japan's choice of a promotion-based statute over the EU model also illustrates the limits of the Brussels Effect in Asia. The article argues that the central problem is establishing how delegated authority can be proven, bounded, monitored, challenged and enforced. Three hypothetical cases test this framework, and six recommendations are matched to the legal routes and institutions needed to implement them. Working paper, version 2.4 (27 October 2026), revising version 2.2 (DOI 10.5281/zenodo.23683437). Version 2.4 shortens the abstract, adds a discussion of AI regulation in Asia and of related literature, and adds sources. Use of AI tools: the author used Claude (Anthropic) to assist with drafting, editing, critical review, and the identification and checking of sources. The author verified the cited sources and takes responsibility for the manuscript's arguments, citations and final text.