Nathan (Jacob Lince), a twenty-four-year-old autistic man, lives with his opioid-addicted nineteen-year-old sister Laura (Madison Ford). Nathan is obsessed with finding his kingdom, a magical land free of fear, hunger, and pain, and has built an elaborate mythology around it. Laura struggles to care for him and is on the verge of committing him to an institution, but instead Nathan talks her into accompanying him on a road trip to find the kingdom.
Nathan's Kingdom contains examples of:
- Abandoned Mine: Nathan and Laura travel through one, leading to an animated sequence where they try to avoid getting eaten by the ghouls that inhabit the mine.
- All There in the Script: According to the credits, the protagonists' parents are named Hope and Angus. Neither one is mentioned by name in the movie.
- Character Narrator: Laura provides occasional narration.
- Cloudcuckoolander's Minder: Laura is under a great deal of strain from constantly having to deal with the trouble caused by Nathan's obsession with his kingdom.
- CPR: Clean, Pretty, Reliable: When Nathan's heart stops during a fight with Evil Condor, Laura yells for help, attracting two passersby, Noel (John F. Henry II) and Jimmy (Peter Mendoza). Jimmy does chest compressions, reviving Nathan in less than a minute, and almost immediately he's running around in perfect health.
- Dedication: "For you, Amélie and Presley."
- Disappeared Dad: Nathan and Laura's father walked out on them after a fight with Nathan when they were about fourteen and nine.
- Functional Addict: Laura manages to hold down a job despite her addiction (at least until Nathan unintentionally gets her fired).
- Guardian Angel: Condor Angel tells Laura that he was her guardian angel when she was a child.
- Happy Place: Nathan's obsession with his kingdom began when Laura told him about her kingdom, where she has lots of friends and can do whatever she wants, and then told him that everyone has a kingdom.
- A Minor Kidroduction: The movie starts with nine-year-old Laura talking to Nathan about their kingdoms. The rest of the movie takes place ten years later.
- Mr. Imagination: Nathan has filled an entire book with information about his kingdom and created costumes and personas for himself and Laura, and he's constantly seeing things from his kingdom in real life.
- Non-Nude Bathing: Nathan sits in the bathtub, fully clothed, while Laura washes his hair.
- So What Do We Do Now?: The protagonists finally find Nathans's Kingdom, an empty field in the mountains. Laura demands to know what Nathan will do now, since he'll die if he stays up here, but Nathan runs father into his kingdom, where he meets Condor Angel.
- Your Favorite: When Laura meets Nathan at the institution where he now lives, she brings his favorite: piles of junk food.
