Rai, also called Rai-chan, is a baby devil boy who appears as a supporting character in Chibi Devi! and attends the same nursery as the main infant, Mao. His devil nature is visible through two small wings on his head and a tail, and his blonde hair and light blue eyes give him an appearance reminiscent of a foreign child. His usual clothing is a yellow-green, or lime green, baby outfit with a light blue bib trimmed in dark blue. When wearing a special costume consisting of a pink wig with a small hat and matching animal-print shorts, he gains the ability to throw electricity.

In terms of personality, Rai is a well-behaved child who usually acts more mature for his age, though he can be quite mischievous at times. His catchphrase is a soft "Fu~", and his laugh is notably old-fashioned, resembling the chuckle of an elderly man; the human characters are initially startled by it, though Shiori eventually comes to find it rather cute. He also has quirky preferences, such as a taste for melon soda poured over rice, and an unpredictable streak: in a scene where the babies are choosing a name, Karin suggests food names while Rai inexplicably wants to use the human name Yoko, which becomes Noriko in the anime.

Rai is raised without a father figure, and a butler helps take care of him instead. He is the adopted son of Shiori and a nursery companion of Mao, taking part in the everyday adventures of the baby devils alongside them. Because his role is that of a supporting figure, the available information about him centers on his appearance, mannerisms, and daily interactions rather than on deep personal growth. His motivations are presented simply, in line with his baby status: he acts on childish impulses, whether that means helping his friends, playing, or causing mischief. Detailed accounts of his long-term development and inner motivations are not well documented, so his characterization remains mostly defined by his mature-for-his-age demeanor, his playful side, and his signature electric ability.