The series is set in XVII-century feudal Japan. Usagi is a ronin - a masterless samurai - and a musha shugyo, a pilgrim-warrior, on a quest to better his spirit and hone his swordsman skills. His skills are already great and his honor and dedication to bushido, the warrior's code - almost unshakeable but his journey has no end.
During his travels Usagi faces countless enemies - different clans of ninja warriors; thugs, thieves and brutes; pawns of the dark lord Hikiji and, last but not least, Jei, an immortal demon - or the messenger of the gods - or simply a dangerous lunatic.
Usagi has many friends too - like Gen, a somewhat surly bounty hunter (and a rhino); Kitsune (a fox), a cheerful and sexy (in a disturbing, animalistic sort of way) con-artist; Chizu, a female ninja warrior with a crush on Usagi; finally, Tomoe - a female samurai warrior who's in love with Usagi (mutually; love, however, would get in the way of their duties and that cannot be allowed.
Both Chizu and Tomoe are pussycats by the way.
Oh, and don't think that with so many hotties around Usagi's a fag who didn't get any. He has a son - so that's at least once.
That's Usagi Yojimbo allright.