Publicly known as Eren, Elyun Grimwald appears human and adventures with Kaval's Party. She possesses a fair stature, blonde hair, and blue eyes in the manga or green eyes in the anime, with distinctive markings under her eyes. Magic conceals her ears, and she wears practical travel clothing, often with a blue tie-on headband.

Born to Archduke Erald Grimwald of the Sorcerous Dynasty of Sarion's royal family, she studied at the Royal Capital Academy before leaving Sarion seeking freedom, accompanied by her bodyguards Kaval and Gido. Her personality is cheerful and positive, though occasionally selfish. A strong sense of compassion and empathy drives her, compelling her to ease others' suffering even if it means revealing national secrets, such as prioritizing aiding friends over state confidentiality. She forms bonds readily, quickly welcoming Shizu into the party and befriending Shuna and Shion in Tempest. Loyalty defines her relationships, and she maintains an open, welcoming demeanor.

Her adventures included investigating the Storm Dragon Veldora's disappearance, using invisibility spells to explore his cave. After this mission, Fuze granted her party three days rest before assessing the Forest of Jura. During this respite, they met and recruited the masked Shizu. They later faced Giant Ants and Salamanders, collaborating with Rimuru Tempest. Following Shizu's death, her party accepted Rimuru's absorption of Shizu and paid their respects before departing with new equipment from Kaijin. They later returned to guide others to Tempest after the Orc Lord's defeat.

Elyun concealed her elven heritage throughout her early appearances, her true nature only revealed during the "Demon Lord Awakening" arc. This concealment occurred despite her royal father's intentions for her safety, though her guards were not elves. Within her party, she frequently assumed de facto leadership, making wiser decisions than the nominal leader Kaval.