Filli is a small, furry creature and a loyal companion to the wild girl Jasmine. He is one of two animal friends she keeps, the other being a raven named Kree. Filli is a male of a species known as Siskis, which are described as being highly intelligent, tiny, bright-eyed, and fur-covered. In the books, his fur is described as grey, while in the anime adaptation, his appearance changes to a white or blonde color, and he is depicted as a small, fuzzy, greenish-yellow creature with a tail.

Filli’s background is tied directly to Jasmine’s own origin story. When Filli was a baby, he was paralyzed by the venom of the Wenn, a hostile tribe living in the Forests of Silence, and was left as an offering to a monster called the Wennbar. Jasmine discovered him there, gave him the antidote to the venom, and saved his life. Since that moment, Filli became one of her closest companions and a member of her adopted family in the forest, alongside Kree.

Personality-wise, Filli is intelligent and perceptive, often displaying a keen awareness of danger that others might miss. He is naturally curious but also cautious, quickly retreating to the safety of Jasmine’s shoulder or hiding behind her thick black hair when a threat appears. Despite his small size, Filli is incredibly brave, especially when it comes to protecting those he loves. He is fiercely loyal to Jasmine, willing to risk his own life to defend her against much larger and more powerful enemies, such as when he attacked a giant Orchard Keeper bird that was stalking her. He communicates primarily through a series of chittering and chattering noises.

In the story, Filli accompanies the main party on their quests across the land of Deltora. His small size and sharp senses allow him to be helpful in various situations. He can climb trees to scout for pursuing enemies and once used his tiny, sharp teeth to bite through a net, helping his friends escape a trap set by the monstrous children of Thaegan. He also seems to be unaffected by certain types of magic, as he was immune to the waters of the Dreaming Spring, which did not affect him because he possessed no evil will.

Filli’s most significant relationship is with Jasmine, whom he considers his family and surrogate mother. She saved his life, and he follows her unquestioningly. Their bond is so strong that Jasmine once refused to leave the dangerous city of Noradz without him, and Filli was struck with grief when forced to obey her command to leave her side during a perilous moment in Shadowgate. He also shares a close bond with Kree. The two animals look after one another and coexist without jealousy, both sharing a deep love for Jasmine. Over time, Filli also grows close to Jasmine’s human companions, Lief and Barda, developing a particular loyalty to Lief, for whom he once safeguarded a precious locket.

Throughout the series, Filli develops from a rescued, passive pet into an active and courageous member of the questing party. While he begins as a creature who mostly hides, he repeatedly demonstrates a willingness to fight, using his sharp teeth to bite enemies and even diverting the attention of guards so his friends could escape. His notable abilities include his sharp bite, his intelligence which allows him to understand complex commands from his human companions, his natural climbing skill, and a perceptiveness that helps warn the group of hidden dangers and magical disguises.