Koromaru is the Persona 3 version of the famous Greyfriars Bobby in Scotland. Bobby was a Skye Terrier who became known throughout the city of Edinburgh during the late 1800s; after his owner died from tuberculosis, Bobby remained in the cemetery for 14 years, faithfully waiting to see his master again.
Koromaru once lived at a shrine on Iwatodai Island with his owner; Shadows killed his owner, but Koromaru stayed at the shrine nonetheless, waiting faithfully, until the Specialized Extracurricular Execution Squad (S.E.E.S.) comes along and adopts him.
Unlike Bobby, though, Koromaru isn’t real. That key difference means his strength of heart lets him summon a Persona — Cerberus, of course — to take the fight to the Shadows.
He’s one of the only party members with a natural defense against dark magic, has high speed, and lands critical hits often, which lets you get that sweet, sweet “One More” extra attack. Like Repede, Koromaru wields a knife in his mouth.
But more importantly, he wears an unbelievably adorable pair of tiny wings and a T-shirt.
His floofy cuteness actually plays an important role in the story as well. Koromaru keeps Shinji Aramaki from being the stereotypical gruff character with no depth, as he’s the only one Shinji opens up to and acts like a normal human around.
That’s a very important point to note later on, before the very bad thing happens ,and you learn more about Shinji, Akihiko, and Ken’s intertwined past.
He also helps you raise Social Link points with others by taking him for a walk at night. Truly, no one can resist Koro-chan’s charms.