The global tax landscape is experiencing a historic transformation as countries implement the OECD/G20’s Pillar Two framework—an initiative designed to introduce a Global Minimum Tax (GMT) of 15% on large multinational enterprises (MNEs). Japan has taken a proactive role in adopting and legislating this framework, aligning its domestic laws with the OECD’s model rules while tailoring certain elements to suit its national tax policy objectives. This article provides an overview of the Income Inclusion Rule (IIR), Undertaxed Profits Rule (UTPR), and Qualified Domestic Minimum Top-up Tax (QDMTT) as implemented in Japan, highlights key dates, compares Japan’s approach with OECD recommendations, and explains the rules’ impact on Japanese corporations.