The opposite of "most nonrealistic" would be "most realistic." Realistic refers to something that is practical, believable, and true to life. It means that whatever is being described or portrayed is based on reality, as opposed to something that is purely imaginary. The concept of realism is often used in various fields, such as literature, art, and film. In literature, realistic works are those that depict real-life situations and characters, while in art, realistic paintings and sculptures aim to represent nature or human figures accurately. Therefore, the antonym for the term "most nonrealistic" is "most realistic.