Hinata Yume is the central human character of the anime, beginning the story as a twelve-year-old first-year junior high school student. Her life changes when she discovers a mysterious, talking plush kitten named Mew that has fallen from the sky, an event that designates her as a Dream Partner. By the second season, Mewkledreamy Mix!, she turns fourteen years old in its nineteenth episode. Physically, Yume has long, light blonde hair that frames her face with curls, and she is almost always seen wearing a lilac plaid headband decorated with a heart-shaped clip on the side. Her standard attire is her school uniform, which consists of a white shirt, a dark pink pleated skirt, a red ribbon, white socks, and coffee-brown shoes.

Yume has a bright, cheerful, and highly energetic personality, though she is also known to be a bit of a clumsy scatterbrain, which can sometimes get her into trouble. She is an optimistic girl who faces challenges with a positive attitude, even when she struggles academically, particularly failing in mathematics. She has a notable dislike for cherry tomatoes and an avid interest in fashion, with a clear preference for the color pink, which is reflected in many of her belongings. Outside of her dream-related adventures, Yume is an active member of her school's cheerleading club and enjoys following the manga titled Cheer Ciao.

Yume's primary motivation is initially driven by a proclamation from the queen of the Miracle Dreamy Kingdom, who appears in her dreams and tells her that if she and Mew collect enough Dreamy Stones, one of her wishes will be granted. This mission forms the core of her role in the story, as she partners with Mew to perform Dream Synchro, a powerful ability that allows them to enter the dreams of others. Within these dream worlds, they work to collect Dreamy Stones and purify the nightmares or "Black Abysses" that appear. As the main protagonist, her role evolves over time, culminating in her becoming the "Princess of Dreams" in the forty-eighth episode of Mewkledreamy Mix!.

Her relationships with those around her are central to her development. Her closest and most important partnership is with Mew, the sentient plush kitten who accompanies her on all her missions. At school, she is friends with fellow Dream Partners Maira Tsukishima and Kotoko Imai, whom she greatly admires and respectfully calls "senpai". Their group later expands to include the transfer student Tokiwa Anzai. A significant relationship is with Asahi Minamikawa, her neighbor and childhood friend. While she is initially unaware of his romantic feelings for her, Yume gradually develops reciprocal emotions for him, creating a key romantic subplot. Her personal growth in this area is also marked by moving on from an initial crush on an older boy named Haruhito Sugiyama, eventually coming to support his relationship with another girl, Yuri Sawamura, after overcoming her initial jealousy. Her family includes a kind and supportive mother, a father who is an avid stone collector, which influences Yume's own knowledge of geology, and a younger cousin named Nana.

Throughout the series, Yume shows clear character development. Early episodes focus on her adjustment to her duties as a Dream Partner, balancing dream purification missions with her everyday life as a middle school student and cheerleader. Her emotional maturation is highlighted by her evolving understanding of romance, from harboring a simple crush to developing genuine, reciprocal feelings for Asahi. Key moments include her learning to handle feelings of jealousy when other girls show interest in him. As a Dream Partner, her notable abilities extend beyond Dream Synchro. When she and Mew enter a dream, she also takes on a transformed "Dream Form," wearing a special baby pink dress with white accents and star-themed accessories, which signifies her active role within the dream world.