Clara is a spotted lagoon jellyfish (*Mastigias papua*), native to the southern Pacific Ocean. Tsukimi Kurashita rescues her from a pet store, where she was housed with a poisonous moon jellyfish. Kuranosuke Koibuchi assists Tsukimi in confronting the store clerk. Clara becomes Tsukimi's pet, residing in a tank within Tsukimi's room at the all-female Amamizukan apartment complex.

Visually, Clara features light pink skin with dark pink spots in certain artwork, characterized by distinctive ruffles and facial features. She serves as a profound emotional anchor for Tsukimi, connecting her to childhood memories of visiting aquariums with her late mother. These memories forged Tsukimi's association of jellyfish, with their lace-like tendrils resembling elegant dresses, with princesses. Clara's presence reinforces Tsukimi's passion for marine life and indirectly inspires her artistic pursuits.

Beyond being a pet, Clara becomes the namesake and muse for Tsukimi’s jellyfish-themed dress designs. These designs evolve into a fashion line created to raise funds to save Amamizukan from redevelopment threats, a consistent plot point across manga, anime, and live-action adaptations. The live-action film's closing credits show Clara's tank gaining a second jellyfish, symbolizing Tsukimi’s emotional growth. In the manga climax, Tsukimi makes personal sacrifices to ensure the apartment’s safety, indirectly securing Clara’s presence.

The name "Clara" originates from "Kurara," a pun on "kurage" (Japanese for "jellyfish") referencing the character Clara from "Heidi of the Alps." Scenes occasionally show Tsukimi wearing clothing bearing the name "Kurara." As a non-anthropomorphized animal, Clara has no dialogue, personality traits, or direct development; her significance lies in her symbolic and narrative functions across all media.