The Piano Sonata is Kishio Hirao's only piano solo work, composed in 1948. This work, which exquisitely fuses modes imbued with Japanese sentiment and the intricate compositional techniques of modern French music, is a masterpiece unique to Hirao and likely one of the representative masterpieces among contemporary Japanese piano sonatas. At the age of 41, Hirao had formed the composition group "Chijinkai" with Komei Abe, Saburo Takata, Kiyohiko Kijima, and others, and was actively publishing chamber music works. Premiered by his wife Taeko, who was a pianist, it is said that Hirao wrote this piece as a confession of his state of mind, as he was troubled by his relationships with women.

The piece consists of three movements, with the first and third movements in sonata form. Particularly striking is the vivid contrast between the intense first theme and the sweet second theme in the first movement. At the beginning of the score, the composer himself inscribed the following words:

Composer's Notes on the Movements

• First Movement: The struggle of a soul battling anguish and anxiety
  Even lyrical sunlight, shining for a moment, is covered by dark storm clouds.
• Second Movement: A slowly sung confession of the soul, gradually rising to a climax, then ending sadly.
• Third Movement: A dizzying world of speed and motion.