Frog Ruru is the twelfth and youngest guardian angel protecting Gorō Mutsumi. Her past life was as a pet frog rescued by Gorō and a young girl from dissection by the girl's father. Though cared for by both, the frog escaped and died from the cold one summer, resulting in Ruru's cryophobia and frigophobia in her current form.

Standing 115 cm tall with a yellow-green motif, her measurements are B:57/W:52/H:62 in the first season and B:60/W:53/H:63 in the second. Ruru exhibits a spoiled, attention-seeking personality, often appearing bratty though not malicious. She is fiercely opinionated yet quick to forgive, ensuring conflicts involving her are short-lived. Her hobbies include climbing and childlike behaviors like hugging trusted individuals. She expresses a desire to marry Gorō, mistaking her deep admiration for him as a father figure for romantic affection.

Ruru is deeply attached to Gorō and constantly seeks his physical affection. She shares a generally harmonious relationship with Momo, seeking comfort from her and engaging in playful teasing. Her interactions with Nana involve frequent clashes, particularly over trivial matters like puppet play, but they reconcile quickly, especially when united by common dislikes. Green is her favorite color and spaghetti her preferred food.

She consistently fulfills her guardian angel role, supporting Gorō while navigating her fears and relationships.