To the Japanese your sword is your soul, it is also your ken, that which you understand. For the Zed your soul is your philosophy, your psyche, your gestalt, your understanding of the world which is not the world itself, but you exert an influence on yourself to make your understanding of the world equal to the world, a simulacrum of the world. Psychopaths don’t have souls because their philosophy is arbitrary, it can only be used to make themselves correct.
The Western soul is double edged showing that it applies to the person wielding the sword as well as to the person they are using it against. Kissing the double edged sword is a metaphor that has been lost in the West. It means that your philosophy can be used against yourself as well as it can be used for yourself. This is known as praxis, walking your talk, living your philosophy. Praxis makes perfect. Your philosophy informs your behavior instead of your desires informing your philosophy.