This book, the final instalment of a four volume series, examines the fifth Pinan / Heian kata. With practical application drills based on both the study of the reactions of students to common forms of aggression and violence in high pressure scenario simulations and years of research into violent crime, it contains a look at some of the myths surrounding the purpose and application of kata, along with a review of the rationale for using interlocking drills to progress from static to dynamic training, and an illustrated discussion of the difference between form and function in training for flexibility, fitness, and fighting. Volume Four approaches the fifth kata (Heian / Pinan Godan) by looking at the common factors that unite effective combative approaches rather than focusing on minor stylistic differences, and as a result provides applications and training drills suitable for everyone, regardless of style or grade. The clearly illustrated application drills teach karateka how to close and create distance while moving freely between the kata's ballistic and grappling techniques. The Pinan Flow System refers to the ability to train karateka to flow seamlessly between ballistic and grappling responses using techniques and tactics embedded in the kata, and illustrates why the Pinan / Heian set, practiced by so many karateka, are an important and misunderstood part of the legacy of Okinawan karate to modern martial artists. Far from being simply kata for beginners, they reflect the distillation of the knowledge and tactics of the father of modern karate, and are an essential training tool and technical manual for beginner and black belt alike.