The document outlines the transition of Rakuten Card Co., Ltd. from outdated core systems to modern architectures using Java EE 7 and Apache Spark, detailing the challenges faced, strategies implemented, and improvements achieved. It describes the development of new core systems that allow scaling and better security while eliminating vendor lock-in through the use of open-source technologies like Payara. Furthermore, it emphasizes the standardization and optimization of the system architecture for enhanced business operations and customer-centric services.