Mokona is a small, white, rabbit-like creature with long ears, elongated feet, and a small, often overlooked tail. Its most distinctive feature is a round, red gem set into its forehead, though this gem has also been known to glow in other colors such as blue, green, and yellow depending on the situation. The creature's body shape is notably elastic and bouncy, a characteristic that is observable in its movements.

In personality, Mokona is a blend of affectionate, cute, and mischievous traits, making it an ideal companion for an adventure. It spends its time assisting the Magic Knights, often teasing Umi and the fairy Primera for its own amusement. Despite its tendency to avoid direct confrontations with monsters, Mokona genuinely cares for the well-being of the three heroines, Hikaru, Umi, and Fuu, and has been known to express sadness or concern for their safety. On one occasion, it bravely sacrificed itself to protect Hikaru from capture, demonstrating that its loyalty outweighs its instinct for self-preservation. The character tends to get along well with Presea, who often joked about punishing Mokona for making a mess in her study.

Mokona’s primary role in the story is to provide for the Magic Knights during their quest in the magical land of Cephiro. Using the power of the gem on its forehead, it is able to magically conjure food, create shelter such as a miniature hotel room, and produce transportation to help the knights cover great distances. It also serves as a vital communication link, as Guru Clef can use Mokona’s gem to project messages and images to the knights. For the most part, Mokona is not a combatant and remains on the sidelines during battles, observing the Magic Knights as they fight. It is unable to speak a human language, communicating instead with cheerful sounds.

Mokona’s background is initially mysterious. It was entrusted to the wizard Clef by Princess Emeraude when she decided to summon the Magic Knights. Clef later gave Mokona to the inventor Presea, who then introduced the creature to Hikaru, Umi, and Fuu. In the manga, a much grander origin is revealed. Mokona is later shown to be the creator of both Earth and the world of Cephiro, having created the latter and its Pillar system after witnessing the devastation of war on Earth.

Key relationships exist between Mokona and each of the three Magic Knights. Hikaru shares a particularly close bond with the creature. She often sleeps beside it and is one of the few who seems to understand its wordless communications instinctively. Umi, on the other hand, has a more playful, teasing relationship with Mokona, often chasing it around or being chased in return. Fuu is more formal in her interactions, being the only one to address it as Sir Mokona. The fairy Primera also has a notable dynamic with Mokona; the creature is protective of Hikaru and will intervene when Primera becomes jealous, often by sitting on her or otherwise distracting her.

In terms of character development, Mokona’s behavior changes subtly over the course of the narrative. It begins as a cute and chirpy creature similar to a wild animal but gradually transitions into a more easygoing and relaxed companion. In the manga, the character undergoes the most significant change at the climax of the story. After Hikaru decides to abolish Cephiro's Pillar System, Mokona returns to its adorable form and then departs from Cephiro along with the three Mashin, or Guardian spirits, to travel to another universe. It should be noted that the anime adaptation handled the character differently; Mokona was not revealed to be the creator of worlds and ultimately remained in Cephiro at the end of the story.