Twenty-five years have passed since Akio Kusano's son, Koichi, dropped out of high school.

During that time Koichi, now 42, has rarely left his house, despite clinging to a dream of one day becoming a rakugo comic storyteller.

According to a recently released government survey, an estimated 541,000 people aged between 15 and 39 in Japan avoid social contact and shut themselves in their homes.