Josh is described as thoughtful, loving and complex. Josh's interactions with the other survivors tend to be humorous. However Josh appears to have Psychosis, a mental illness characterized by a disconnection from reality. If the Psychiatric Report is found during Chapter 7, it's revealed that Josh has been suffering from his mental illness since he was 11 years old. However, all medications that are listed in the record are for depression treatment, which is not what Josh was suffering from.
He cares for his friends, acts as a brotherly figure to Chris, and likes to make sure everyone has a good time. He shows affection towards Sam. His dreams of following his father's footsteps in becoming a film producer makes him very knowledgeable about special effects and movie props and as such, he constantly uses phrases and words from movies.
He struggles to come to terms with his sisters' disappearances. The event triggered depression, which became more and more severe a year prior to the events of Until Dawn.