Koromaru is the only known dog with the ability to summon a Persona. He awakened while fighting a wayward shadow, and got severely injured in the process. He is taken under the care of SEES and later joins them upon making a full recovery. Koromaru is trained in the use of battle knives, kunais and blade masks. His Persona uses Dark powers in conjunction with Fire spells.
 In Game
Koromaru first appeared in front of Iwatodai Dorm, playing with Yukari Takeba and Fuuka Yamagishi. A passing housewife tells them that Koromaru lives by himself nowadays since his master, who was a monk at the Naganaki Shrine, recently died in an accident. Koromaru often takes walks around town like he and his master used to do, except now, he does it all alone.
Akihiko Sanada is the only one to witness Koromaru's awakening while out on night patrol. He is impressed by the promise the brave dog shows, and Mitsuru Kirijou takes it upon herself to give Koromaru the best treatment possible for the injuries he sustained from fighting the shadow in the shrine. Upon recovering, Koromaru joins SEES on his own accord to return the favor. He is given clothes (with decorative wings) for protection, and a special Evoker collar that allows him easier access to his Persona.
If you were able to meet with Akinari Kamiki prior, the missing red fountain pen that he is asking you to find will be in Koromaru's possession. You can take it from the dog at any given evening in the dorm.
While Koromaru cannot actually talk, Aigis serves as an interpreter to him, being able to translate his thoughts into human language. As special as he is, Koromaru still behaves like any other dog who needs his occasional nightly walks and begs for any kind of attention from the people who are looking after him. He usually prefers to hang out with Aigis, because she is the only one who understands him, Junpei Iori, who he has known for a long time, and Shinjirou Aragaki, who often spoils him with home-cooked meals and high-grade dog food.
 Let's Take Koro-Chan For A Walk!
In FES, you have the option to walk Koromaru on certain evenings, often going to play in Naganaki Shrine which was his former home. You'll know that he's in the mood for a walk when he looks at you pleadingly.
If you go with him alone, Koromaru will dig up some random consumable items to pass on to you, and sometimes you might run into a few S. Link characters in the process (this will help to deepen your relationships with them). There are also instances when a fellow SEES member can even accompany you, usually before or after a story sequence.
- Koromaru's character design and personality seems to be based off of Hachiko, a loyal dog who always waited for it's master to come home from work for 10 years even after he had already passed away. The dog eventually died, but was later immortalized in a statue erected near Shibuya station, the same place where Hachiko was often seen.