Pascal is the protagonist's domestic dog, which stays at his home until the assassination of his master's mother at the hands of an Amanojaku, whom the protagonist then defeats. Pascal will then be available to enter the protagonist's party, and if fused with any demon at a Cathedral of Shadows, the result will be an extremely powerful Cerberus, that can be created independently of his far superior level only because of his former loyalty towards his owner. Following the events of the Echo Building arc, where the protagonist goes to check the Terminal used by Gotou's scientists in order to summon more demons to Tokyo, Pascal/Cerberus jumps into a Terminal after the boss fight against Douman and is teleported to an unknown destination.
Much later in the game, he reappears (automatically transformed to Cerberus if the player did not already do so), standing on the bridge that leads to Tokyo Destinyland, in a berserk state that can only be reversed if the protagonist possesses a valuable item called a Golden Apple. Because of this item's ability to stabilize violent demons, Cerberus comes back to his senses and recognizes the protagonist, thus choosing to share his fate by joining his party.
In the Sega CD version of Shin Megami Tensei, Pascal's design is heavily reworked into a unique version of Cerberus that looks more like a combination of the series' traditional design with a normal dog. He also changes heavily in design between his absence with the protagonist.
Pascal, still as Cerberus, survives the death of his first master, and eventually meets and becomes friends with Madam. When Aleph receives his first quest from Madam, Pascal joins him to assist in finding Haneda, and leaves the party when the mission is complete. Later, after Abaddon swallows Valhalla, he is found in the underground passage near the former entrance to the city and joins Aleph once again.
If the protagonist dies during a Full Moon, there's a 1/256 chance of them getting a rare Guardian, which has 25% of chance of being Pascal.
Pascal is a rare encounter on fixed locations just like the Fiends, though he can't be encountered if the player already has him as a Guardian. Pascal will at first try to run away, and the protagonist needs at least 25 Agility to catch up to him and initiate the battle.