Jotaro is the son of Miyamoto Usagi, but due to circumstances they do not acknowledge it; they treat each other as uncle and nephew, and neither is aware that the other knows the truth. Jotaro is currently training to be a samurai and has displayed formidable skill for his age; he has defeated adult opponents with his bokken in single combat, despite his still small stature.
Before leaving to serve Lord Mifune, Usagi had a tryst with his childhood love, Mariko, which led to them conceiving Jotaro. Mariko later discovered she was pregnant. Kenichi, who was also in love with Mariko, convinced her to marry him, so that she would not be dishonored by having a child out of wedlock. Kenichi treated Jotaro as his own child, and genuinely loved as if he were so, but it is one of the many sticking points between Kenichi and Usagi. For his part, Usagi had no idea about fathering a child, and Mariko refused to tell him so as to not make him feel obliged to resign his post and return to her. In Circles, just as Usagi is leaving the village, Mariko tells him the truth about Jotaro, and instructs him not to reveal it to Jotaro, for fear that it would alienate Jotaro from Kenichi.
