Eruka Frog is a witch from Soul Eater whose design and magical abilities center on a frog motif. This theme is reflected in her appearance, which includes long, straight silver hair, a narrow mouth with dark spots at the corners that resemble a frog's air sacs, and a distinctive orange hat shaped like a frog's face that can even mimic her own expressions. Her typical clothing is a black, white-polka-dotted dress worn over a dark blouse, paired with black pants and knee-high white boots.

As a witch, Eruka possesses a range of magical abilities tied to her amphibian theme. She can use Transformation Magic to change into a small frog, a form she often employs for spying or escaping danger. Her primary offensive magic is the Tadpole Bomb, which allows her to create small, hopping, tadpole-like creatures that explode on command or upon impact. She also has a talent for Calculation Spells, a type of magic that uses complex mathematics to act as a placeholder for other high-level spells, ensuring they are more precise. Like many witches, she can use Soul Protect, a spell that hides her true magical nature and makes her soul wavelength appear to be that of a normal human. Despite having these skills, she is considered a witch of relatively low caliber and possesses far less destructive power than more formidable witches such as Medusa Gorgon.

Eruka's personality is defined by a mixture of witch-like pride and overwhelming cowardice. Like many of her kind, she enjoys the inherent destructiveness of being a witch, but she is extremely fearful and will almost always choose to flee from a fight, readily begging for her life when threatened. She can be demeaning to those she considers beneath her, yet she is not entirely cold-hearted. Unlike the more malevolent Medusa, Eruka displays regret and consideration for others, such as when she feels guilty for lying to her friend Mizune's family or tries to reassure Crona during a difficult mission. This cowardice is a driving force in her life, as it often places her in servitude to those more powerful than herself. After a failed attempt to kill the witch Medusa Gorgon, Eruka had several of Medusa's magical snakes implanted in her body, a constant threat that forces her into reluctant servitude, as Medusa can activate them at any time to tear her apart from the inside.

Throughout the story, Eruka acts as a begrudging agent for Medusa, tasked with various dangerous assignments. A key mission is breaking the immortal werewolf, Free, out of the Witch Jail, after which he becomes her frequent companion and partner. Despite her resentment toward Medusa, she works alongside Free on subsequent operations. As Medusa's schemes escalate, Eruka is forced to participate in the infiltration of Death City to help revive the kishin Asura, eventually becoming a prisoner of the Death Weapon Meister Academy. She has a close friendship with the mouse witch Mizune, though her regret over deceiving the younger Mizune sisters for a mission shows the strain her coerced role places on her personal relationships. Eruka also has a genuine and affectionate bond with her giant tadpole familiar, Otama Jackson, and becomes angry if anyone hurts him. Her most significant relationships are defined by fear and obligation, particularly with Medusa, whom she both resents and fears, and a more willing partnership with the powerful but clumsy Free. Her role eventually evolves as, after Medusa's apparent death, she is forced to cooperate with the DWMA, marking a shift from a minor antagonist to an uneasy, reluctant ally.