What vivid image does Tanimura create to depict the character of Kitaru in the first few lines of the story "Yesterday"?

When describing Kitaru's uniqueness in the first few lines of the story "Yesterday," Tanimura creates a vivid picture of Kitaru in the bathtub as he belts out fake lyrics to the Beatles's song Yesterday in Japanese. The reader receives a clear picture of Kitaru's boisterous and fun-loving nature, qualities that will come to the forefront of the story later in the narrative.