Ward D takes place in a locked psychiatric ward and features multiple patients diagnosed with schizophrenia, bipolar disorder, or both. While these mental health conditions are often stigmatized, they are not inherently linked to violence, as perpetuated by horror and thriller media, though they do pose unique challenges. Ward D engages with such established and stigmatizing tropes to drive the events of the plot.

Schizophrenia is a mental health condition marked by hallucinations and delusions. There is no test to diagnose it, with diagnoses usually being based on patient reports and observations by physicians and other witnesses. Most people with schizophrenia begin showing symptoms as teenagers or their early twenties. Men are more likely to be diagnosed with schizophrenia than women, and symptoms tend to show earlier in men. Treatment usually involves antipsychotic drugs, therapy in the form of psychiatric counseling, and social rehabilitation. Most people will show improvement in symptoms with no relapses; however, there are those who will experience symptoms for the rest of their lives.

Bipolar disorder is a mood disorder marked by a cycle of depression and mania. Periods of depression are marked by deep sadness that often includes suicidal ideation; periods of mania are marked by a euphoric or irritable mood that often includes erratic thinking and impulsive behavior such as compulsive shopping.