The Soft Bow Stance can be considered a modified Zenkutsu Dachi in which the back leg is bent rather than straight. In the Soft Bow the degree to which the back leg is bent can vary greatly from a slight bend to a significant bend in which the knee is held fractions of an inch from the floor.
This stance is often used to gain rapid access to an opponent’s lower extremities for the purpose of striking or manipulating their structure. As such it is always executed as a transitory stance during a conflict.
The stance is often held statically however as a way of building leg strength. When performing the stance for this purpose the front leg is bent severely (but the knee does not go forward of the ankle) and the back leg is bent and lowered until the back knee is only an inch or so from the floor. This is a very difficult stance to hold.