Ram serves as a maid alongside her twin sister Rem at Margrave Roswaal L. Mathers's mansion, identifiable by her light pink hair covering one eye, darkish red eyes, and standard maid uniform. Born into the Oni Clan as a prodigy with a single horn, she possessed immense combat strength and mana manipulation, revered as the Oni God's reincarnation. However, these powers came with escalating violent impulses. Protecting Rem during a Witch Cult attack on their village resulted in Ram losing her horn, permanently weakening her and eradicating her bloodlust. Rescued by Roswaal, Ram pledged service in gratitude, though she initially harbored vengeance against him for his indirect role in the massacre. Over ten years, this hatred transformed into devoted love.

Despite her diminished power, Ram maintains a sardonic, self-centered exterior and often appears lazy or performs tasks poorly due to chronic pain from her severed horn. She secretly handles the Mathers Domain's administrative duties during Roswaal's absences. Her cold demeanor creates protective distance, though she harbors deep care for those close to her. Ram is fiercely protective of Rem, prioritizing her sister's safety since childhood. During crises, she masks worry with indifference but can become emotionally volatile or violent when trusted individuals are threatened, exemplified by her confrontation with Subaru after he forgot Rem.

The OVA "Memory Snow" depicts Ram's daily life during an unexpected cold spell caused by Puck's magical release period. She sleeps late, dismissing Rem's concern about inadequate clothing. Disturbed by Subaru, she punishes him with chores leading to the discovery of hidden alcohol. Ram teases Subaru by falsely claiming prevention of alcoholism, provoking Emilia to join. Her sarcasm resurfaces when mocking Subaru after Emilia postpones their date. During Puck's prolonged ice magic, Ram huddles by the fireplace with Subaru and participates in the snow sculpture festival. She collaborates with Rem on a snow sculpture merging Roswaal and Subaru's features, which receives low ratings.

Ram retains limited access to her Oni abilities. She can temporarily enter an Oni Form by releasing power "shackles," though each use causes severe physical backlash like vomiting blood and paralysis. Connecting via abilities like Cor Leonis or Rem's horn mitigates this but risks fatal consequences for Subaru or temporary leg paralysis for herself. She requires regular mana infusions from skilled users like Roswaal or Julius Juukulius at her horn's severance point to sustain her body. Ram also possesses Clairvoyance, an Oni tribe art allowing vision synchronization with others sharing her wavelength. Using it causes physical strain like blood-tearing and leg tremors, and fails against individuals who mentally block her or "high-ranking" beings like Roswaal.