This article dissects 'Sekiro: Shadows Die Twice' from a game designer's perspective, focusing on how its core experience—embodying a ninja in cinematic sword fights—shapes every system. The 'deflection' combat system, based on posture and parrying, replaces traditional turn-based action, encouraging aggressive play. Exploration, items, prosthetic tools, and skills all reinforce this core loop while maintaining narrative coherence. The game transitions from RPG to action logic, lowering the skill barrier for traditional action games but limiting weapon variety. Despite this, 'Sekiro' exemplifies how tightly integrated design can deliver a unified, immersive experience.