mamezo

Usagi's ever-present companion and foster child, he appears to be a young boy between six to eight years old. Despite his age, he seems more adept at everyday tasks than Usagi, even assisting her in getting dressed. Mamezo was discovered as an infant by Usagi's dog, Shiro. Hanzō believes that this encounter is the root of Mamezo's fear of dogs. As time progresses, it becomes evident that Mamezo's greatest desire is for Usagi to be his mother and Hanzō to be his father. Eventually, Mamezo meets his biological parents, who reject him; his father attempts to make him forget his past, while his mother admits she cannot love him as much as she loves his younger brother. This leads Mamezo to sever ties with them permanently. Upon learning that Mamezo can never become a court noble, his grandfather entrusts him to Usagi's care. Later on, Mamezo becomes engaged to his childhood friend, Watari, and evolves into a skilled shinobi ninja.
(Source: Wikipedia)