Nikkei Exter Stock Average is a simulated market index developed to analyze and track the movement of the Japanese stock market. It is conceptually inspired by traditional Nikkei-style indices, while incorporating proprietary calculation models and statistical methodologies designed for advanced market analysis and educational use. The Nikkei Exter Index is designed to reflect the overall behavior and structural dynamics of the Japanese equity market from an analytical perspective. By combining historical market data with mathematical and market-simulation models, the index provides insights into long-term trends, volatility patterns, and price movements of the Japanese stock market. Nikkei Exter applies a price-weighted methodology, referencing a representative group of equities associated with the Prime Market of the Tokyo Stock Exchange. The index is intended to support research, education, and system development related to market behavior and financial analysis. It is not designed to serve as an official financial benchmark or investment reference.