Ishida's works feature three major themes: Japan's identity and role in today's world; Japan's social and academic educational structures; and Japanese people's struggles to adapt to social and technological changes in Japanese contemporary life.
Ishida's works convey isolation, anxiety, crisis of identity, skepticism, claustrophobia and solitude. Ishida explored several motifs, including portrayals of school-boys and business-men as a part of a factory and young people as physically integrated with everyday household objects. Though the subjects in this series appear to resemble Ishida's own face, Ishida denied these works were self-portraits.
Ishida shared anecdotes of his parents expressing bewilderment over his art style and the dark nature of his works. His mother was particularly upset by one of his self-portraits as she felt it was too dark, but he assured her that it was him at his happiest because he felt he could communicate better through his painting than he could in person. He later reported that his parents came to accept his works as part of his personality and that they, particularly his father, were able to appreciate his works even though they still didn't understand his art.
In a snippet from an archived television interview used during Tokyo TV's Kirin Art Gallery's feature "The Grand Art Masters", Ishida had stated that regardless of whether he liked painting or not, he felt compelled to continue painting "people at mercy of Japan's contradicting nature of its social systems for as long as they exist".
There are some aspects of his works that still intrigue his art critics. One of most discussed topics is a recurring motif found in the majority of Ishida's works: a plastic shopping bag. Ishida had consistently refused to explain the purpose and the meaning of the shopping bag. With Ishida gone, the question mark over the shopping bag motif is likely to remain for good. [3]