Origami figures

Origami figures play a major role in Heavy Rain, being part of the Origami Killer's modus operandi. When a victim appears, they always have an orchid on their chest and an origami figure in their hand. The Origami Killer sends a box with several origami figures inside of it to the father of the child that has been kidnapped. Each of these are numbered, and, when unfolded, reveal a phrase challenging the father to save his son, along with an address. These lead the father to the trials. After Ethan Mars awakes from a blackout, he is seen holding an origami figure in his hand.

Outside the story of Heavy Rain, the origami figures are used as icons for the game's trophies.

Murder Birds
The Bird is the most iconic origami figure in Heavy Rain. It appears on the cover of the game, as well as several of the game's trophies. When Heavy Rain is being installed onto a person's PlayStation 3, a set of instructions appears on screen, showing the player how to make a bird origami figure, using the paper that is included in the game's box.

The Bear
The Bear is the origami figure that represents the first trial. It represents the creature's violence as Ethan Mars has to drive the wrong way down a very busy highway, possibly ramming into multiple vehicles.

The Bear origami figure appears as the icon of two trophies: Good Driver if Ethan completes the Bear Trial, and Kamikaze if he finds the best possible route throughout the journey.

The Butterfly
The Butterfly is the origami figure representing the second trial. Ethan has to crawl through a dark tunnel filled with glass and through a field of electrical conductors perhaps symbolizing the Butterfly as a metaphor for how fragile the human body is or how fragile Ethan's resolve might be when tested against such drastic odds. It may symbolize the creature's small body size which allows it to squeeze into tight spots, as seen in the first part of the trial where Ethan must crawl through a very claustrophobic area.

The Butterfly origami figure appears as the icon of two trophies: Coward! if Ethan fails the Butterfly Trial, or Electrified if he completes it.

The Lizard
The Lizard is the origami figure that represents the third trial. The third trial is called "The Lizard," most likely because of certain lizards' ability to lose limbs/body parts and live while doing so. Ethan has to amputate his finger, mutilating himself like a lizard could be mutilated. Also, some lizards can remove their own tails if they are caught and in danger, similar to how Ethan must remove his finger to save his son Shaun from danger.

The Lizard origami figure appears as the icon of four trophies:

Gold Finger - Cut your finger using axe, knife or pillars + disinfect or cauterize the wound

Butcher - Cut your finger using saw or scissors

Fugitive - Manage to escape Blake in the subway station

Hands Up! - Get arrested by Blake or Jayden

The Shark
The Shark is the origami figure that represents the fourth trial. The reason that the Origami Killer could have chosen the figurine of the shark might be because of the simple violence of the trial. Sharks are stereotypically violent, murderous creatures, and since some of them man-eaters, Ethan having to murder Brad creates a parallel between Ethan and a shark.

The Shark origami figure appears as the icon of two trophies:

I'm a Killer... - Kill the Drug Dealer

I'm not a Killer! - Do not kill the Drug Dealer

The Rat
The Rat is the origami figure that represents the the fifth and final trial. The Origami Killer may have chosen a rat figurine for the fifth trial because rats' history is usually associated with being carriers of disease, so the poison references their uncleanliness. The room is also synonymous with this, the corridor representing blood and the main room representing cleanliness. The fact that rats were carriers, not sufferers of disease, also hints at the poison being a fake.

The Rat origami figure appears as the icon of three trophies:

Sacrifice - Drink the poison

Clever Dad - Work out where Shaun is being held

Trial Master - Succeeded in all Ethan's trials

The Dog
The Dog figurine can be seen in a few chapters, such as "Shrink and Punches" and "Ann Sheppard." Each time it appears, more information is revealed about the Origami Killer: in the former, Clarence Dupré shows Norman Jayden and Carter Blake what Ethan left behind after their last session; in the latter, Ann Sheppard reveals the killer's identity to Madison Paige. The killer also places an origami dog in the hands of each of his victims, and Ethan awakens from his blackouts holding an origami dog.

The Dog origami figure appears as the icon of two trophies:

Perfect Crime - Clean Manfred's shop of evidence + Let Lauren, Hassan and Kramer die + kill Madison and Jayden + Origami Killer free

I'm not Scared! - Twins - Follow the brother without making any mistakes

Trivia

 * The origami lizards are made in the Kawasaki style.
 * The origami sharks are made in the Nicolas Terry style.
 * The origami dogs are made in the Komatsu style.
 * The origami butterflies, rats, and bears are made in a style that is currently unknown.