Ryuukou Yanagi

The smallest of the convicts physically, he is later being shown as the most deadly. He is the only convict whose crime is known, that he killed a dozen men in prison as a test bed for his new skill. He uses a special martial art called Way of the Void (空道, Koudou). In this style he practices Vacuum Palm, Whip Strike, Poison Hand and many others. Yanagi is also very good at using weapons, such as a rope sickle during fight with Baki Hanma, or the Bagh Nakh during fight with Goki Shibukawa.

(Source: Baki Wiki)