NTT Docomo Business, Ltd. (formerly NTT Communications Corporation, hereinafter referred to as NTT Docomo Business), Toshiba Corporation (hereinafter referred to as Toshiba), and NEC Corporation (hereinafter referred to as NEC) have commenced the construction of a wide-area quantum cryptography communication network spanning approximately 600km, connecting the three major metropolitan areas of Tokyo, Nagoya, and Osaka (hereinafter referred to as the Tokyo-Nagoya-Osaka region). This initiative is part of the efforts by the Ministry of Internal Affairs and Communications and the National Institute of Information and Communications Technology (NICT) towards the social implementation of quantum key distribution. Following its construction, demonstration experiments using this network for quantum key distribution will be conducted. This demonstration aims to foster promising use cases by verifying secure communication using quantum technology, with a view to social implementation in industries such as healthcare, finance, and electric power, which handle highly confidential data including national security information and personal data. 1. Background In recent years, as society transitions towards advanced AI and increased data utilization, the need to collaborate and utilize diverse data, including critical data, across organizations and regions has grown. Concurrently, advancements in quantum computing technology raise concerns about the degradation of the cryptographic strength of existing encryption technologies, whose security relies on computer performance. Consequently, the importance of new communication technologies for long-term secure protection of highly confidential information, as well as secure operation and key management, is increasing. In particular, addressing the "Harvest Now, Decrypt Later" (HNDL) risk, where current communication is intercepted and stored for future decryption by quantum computers, is a critical challenge from the perspectives of na