Manatsu Shiraishi is a second-year student at Takadanobaba Girls' Academy and the jetter of the team Mega Kute Hyper Ultra, commonly abbreviated as MKHU. She is a kuro gyaru, a style characterized by a tanned complexion, back-length caramel blonde hair tied in a ponytail with bangs on both sides, and blue eyes. Her appearance is noticeably more tanned than that of other characters.

In terms of personality, Manatsu is bright and fun-loving, with an energetic and outgoing demeanor. She is a pure-hearted girl who is easily flustered, often becoming the target of suggestive teasing from her teammate and best friend, Yuzu Midorikawa. Despite her occasional embarrassment, she maintains a positive and optimistic outlook and is determined to succeed in jet racing. Her motivations center on a love of fame and fortune, which aligns with her gyaru lifestyle, but she also genuinely enjoys the sport and the camaraderie it brings.

Manatsu's role in the story is that of a supporting character and one of the rival racers. She attends Shinjuku Takadanobaba Girls School and forms the team MKHU with Yuzu Midorikawa. The two are best friends who speak using similar Western-influenced slang and share common aspirations. Their teamwork is tested through the Kandagawa Jet Race tournament, where they compete against the main protagonists, Rin Namiki and Misa Aoi. Manatsu's key relationship is with Yuzu; their bond is central to her character, as they support each other both on and off the water.

Over the course of the series, Manatsu shows development through her growing confidence in her abilities as a jetter. She is quick to learn and adapts well to new racing techniques, demonstrating a natural talent for piloting watercraft. Her notable ability lies in her performance as a jetter, where she handles the speed and maneuvers of the jet ski with skill. Her positive attitude and determination also help inspire her teammates, contributing to the group dynamic within the competitive world of jet racing.