Nankoku inherited his father’s teaching that Sho was the art of the line. In Sho, the line is not immediately subordinate to the meaning of written letters or the literary contents. And also the line is not the expression of the writer’s emotion which he commits to the letter. The line’s form such as its qualities, slow or fast line, curve or straight line, wet or dry line, strong or weak line etc. flows from the variations of the writer’s personality stroking the brush, and the line expresses his inner being. The line of paintings leaves from the outlines of the object, but the line of Sho expresses human inner depth, that is ‘ hitu-i’ (spirit of brush-stroking) in terms of traditional calligraphy.
Nankoku had constantly been criticized by reason that his works did not belong under the Sho owing to staying apart from characters. But Nankoku persisted in his belief that his works were Sho; moreover, they were Sho which inherited the essence of Sho.