The Baby (real name unknown) is a human baby which played a key part in Episode LII: Jack and the Baby.
Revealed to be female during San-Diego Comic-Con, she is cute, has big blue eyes and wears a diaper.
She is very unintelligent (considering it for a baby), very stubborn but understands how Jack communicates with her. However, when Jack told the story of Mamatoro to her, she suddenly changed her expression from a cute baby to an angry baby.
Jack rescues a baby and then tries to find the child's mother while caring for it and protecting it from hungry ogres. Jack retells the story of Momotaro to the baby. After returning the baby to its mother, the mother notices the stern face on her baby. Jack apologizes and explains that he now has Sakai or The Spirit of the Samurai. While Jack walks away onto his next destination, the baby looks on and shouts 'MOMOTARO!'