Mirumiru-chan inhabits a lush forest as a youthful infant milk droplet sprite, embodying innocence with a petite, white droplet-shaped form. Her features include shimmering eyes, faint pink spiral blushes, and a lone eyelash per eye. A pale blue bib labeled "MILK" rests around her neck, paired with delicate light blue wings.

Despite her tiny stature, she wields extraordinary strength, effortlessly lifting objects heavier than herself. A keen sixth sense guides her to milk sources, often driving her to trail cows for their fresh yield. Rain induces rapid growth, occasionally making her tower over fellow sprites. Communication remains limited to soft, infantile sounds like "Nyu~."

Her personality radiates sweetness and cheer, endearing her to younger sprites through playful antics. Though unnaturally strong, she retains wide-eyed naivety and trust. Bonds include a raindrop sprite, a snail companion, a slobber sprite, and an especially cherished skin-lotion sprite.

Her name stems from "miruku" (Japanese for "milk"), reflecting her essence. Family members manage a woodland milk shop. In a human-themed spin-off, she retains her bib, infant traits, and simplistic speech. Official narratives maintain her core attributes without expanding her backstory or development.