Kaeru no Rulu, also known as Lulu, is the 12th and youngest Guardian Angel assigned to protect Gorō Mutsumi. Her past life was as a frog, born on June 21, 1994. In late spring or early summer, Gorō encountered a distressed girl in the woods; she had rescued the frog from her father, a school science teacher. Gorō convinced the father to let his daughter keep the frog, and together they nurtured it back to health, forging a strong bond. During an unusually cold summer day, the frog escaped and later succumbed to hypothermia.

After death, she transcended to the spirit realm but became lost in the void en route. As a Guardian Angel, her emblematic color is a distinctive yellow-green chartreuse. The trauma of freezing to death instilled cryophobia (fear of cold) and frigophobia (fear of cold objects), presenting significant challenges in her duties.

Lulu exhibits a childlike personality, seeking attention and desiring closeness to her master. She displays spoiled or bratty tendencies, like anger when others disagree, though never maliciously. Conflicts involving her are short-lived as she forgives easily. She frequently hugs Gorō and initially dreamed of becoming his wife, though her feelings reflect daughterly admiration rather than romance; she views him as a father figure.

Among fellow angels, she maintains harmony with Momo, often seeking comfort from her. Her dynamic with Nana involves frequent, quickly resolved arguments, such as play disputes ending in mutual apologies. Lulu occasionally teases Momo, targeting her weaknesses. Both Lulu and Nana initially shared a dislike for Daisuke.

Physically, Lulu has green hair and eyes, stands 115 cm (3'9") tall, with measurements B:57/W:52/H:62 in Season 1 and B:60/W:53/H:63 in Season 2. Her hobbies include climbing. Her favorite color is green, and her preferred food is spaghetti.