Shu Kawamura developed Prometheus-based metrics for tracking conference registrants in the cloudnativedaysjp/dreamkast repository, enabling real-time visibility into both online and offline attendee counts. Using Ruby for backend development, Shu integrated Prometheus gauges with the StatsOfRegistrant data source, allowing conference organizers to monitor registration trends and improve capacity planning. The work included targeted code refactoring, specifically removing dead code from DreamkastExporter related to registrant metrics, which reduced technical debt and improved maintainability. This focused contribution enhanced the system’s observability and supported data-driven decision making, demonstrating depth in metrics and monitoring as well as backend engineering practices.