Jason Mars is the son of Ethan and Grace Mars in the game "Heavy Rain" developed by Quantic Dream. He is introduced in the prologue with his brother Shaun Mars.
The prologue of Heavy Rain features the lives of the Mars family members. Jason and the other family members are introduced when they return home from grocery shopping, and they celebrate Jason's birthday. The family goes to the mall where Jason wants to buy a balloon. While Ethan is searching for money to pay for it, Jason takes off with his balloon. When Ethan finds him, Jason has been hit by a car. His death affects the entire family and impacts Ethan the most as it leads up to his current state in the main story arc of "Heavy Rain."