Where not a great deal is known about Kantarou's childhood and the many years that followed, we are given glimpses of an abused past that later defined the person he would become and the many goals and missions he would set in life.
The ability to see yokai (demons/monsters) and spirits is very rare among humans, and for the most part, belief in such creatures is non-existent, even in pre-westernized Japan. Kantarou, however, was born with the ability to see the creatures of the spiritual world, and he came to befriend them. However, due to such, the other children would tease and beat upon him when he spoke of yokai or tried to defend the invisible creatures. He was regarded as an outcast by other children, and his only friends were the gentle yokai of the forest.
One night, after being bullied once more, Kantarou expressed his desire to be stronger as a person so he could defend himself and his many yokai friends. In an attempt to cheer him up, the yokai told young Kan-chan of the legendary oni-kui tengu (ogre-eating goblin), the strongest tengu known to man. Interested and inspired, Kantarou vowed to find the resting place of the legendary tengu and breaks its seal. This became his life-long obsession; to find the one being that gave him strength in pain and sorrow.
The skills and spells Kantarou use are that of historical origin, and speak of family tradition. Where as not all facts concerning the Ichinomiya family are concrete, we are given the impression they hale from a background of strict tradition in the realm of spiritualism and exorcism. The type of exorcism Kantarou uses is taught and passed down through the ages from father to son. This, in turn, gives us the notion of a spiritualist family history.
In addition, it is later revealed that it was an Ichinomiya that sealed Haruka, the oni-kui tengu, many years ago. Kantarou discovered this in his research while searching for its resting place. Fitting that a member of the same family that sealed the yokai would later release it.