Himura Kenshin was orphaned at a very young age when his parents died of cholera, and ended up being taken as a servant by a wandering band of slavers. After, being attack by thefts and now the lone survivor thanks to the help of his new master, Seijuro Hiko (Master of the Hiten Mitsurugi fighting style). Kenshin trains to learn Hiten Mitsurugi but just before he is almost finish his training, he joins the war in hopes to make a difference in the world. During the war he gets the scar-cross on his face adn the nick name Hitokiri Battousai for killing som many people (the guilt). After the beginning of the Meiji era, however, he decides to trade in his daisho (katana and wakizashi) in exchange for a sakabatou (reverse blade). He then swears never to kill again and begins wandering through Japan.
Kamiya Kaoru was the young woman (I _do_ mean young; she's only 16!) who let Kenshin stay with her at her dojo. She is an adjutant master of the Kamiya Kashiin Dojo and is actually quite the swordsman herself. A lot of people think she's weak, but she's actually quite strong. It's just that, compared to Kenshin and Sanosuke, she's bound to come up short. Kaoru also has pretty strong feelings for Kenshin. She sometimes expresses her feelings in strange ways, but otherwise, I think I can solidly say that she cares very deeply for him. Kenshin, likewise, cares deeply about her-- in his own words, in fact, Kaoru has become 'home' to him.
Sagara Sanosuke used to be a member of the Sekihoutai group before the Ishin turned on them and had them all killed. He was just a boy when he watched the Captain of the Sekihoutai, Sagara Souzou and the rest of his soldiers murdered, and he grew up with a lot of misgivings against the Ishin. When he first met Kenshin, he knew him only as the Battousai and thus challenged him to a duel. At first, Kenshin refused, but after a certain series of events ensued, they finally battled. Obviously, Kenshin was the victor and he and Sanosuke eventually become friends. Sano is very loyal and very protective of his friends, and often bites off more trouble than he can chew. He is also quite stubborn and a bit slow on the uptake sometimes, but makes up for it with brute strength and bulkhead determination.
Myojin Yahiko As the best and only student of the Kamiya Kashiin Dojo, Myojin Yahiko is a young boy who met Kenshin and Kaoru when he tried to pickpocket them. A quick learner and versatile student, Yahiko proves to be everything Kaoru wished for in a student and every thing she hated in a charge. Though they don't much show it, the two developed a certain student-teacher, parent-child closeness that is uniquely their own. Yahiko also looks up to Kenshin as a sort of father-figure, and has quite a bit of respect for his strength and kindness. Another character that Yahiko shows a fondness for is the young Tsubame, who works with him at the Akabeko. He is often very gentle with the girl, and makes an effort to be on his best behavior with her. Sano and Yahiko, on the other hand, behave like squabbling siblings whenever they are together, and can often be heard hurling insults at each other.
Takani Megumi is one of the finest doctors in the Tokyo area. Though she generally has a good heart, she is constantly butting heads with the enigmatic Kaoru when it comes to vying for Kenshin's attention. Both women are in love with Kenshin, but with Megumi it's more for show. She also argues constantly with Sagara Sanosuke and more often than not ends up being paired with him. She is really not a fighter, preferring to give medical aid rather than another sword arm during battles.This doesn't make her weak, though, because emotionally, she's quite strong. A member of the Aizu Takanis, Megumi managed to survive through the burning of her house and the loss of her parents and siblings.