The "hero" of the story, Manji is Rin's bodyguard for 4 years. Although he was first reluctant to help her out, he agreed to accompany her into town, and get some practice on real flesh and blood while he was at it. The agreement between the two is that he'll protect her for four years, if she gets hurt during that time the price drops to nothing. Manji will often make jokes about selling Rin into a whorehouse. Not now but maybe in four or five years when he'll be able to fetch a good price for her. He feels guilty at times for not being able to save his sister Machie when she needed him. Rin reminds him of her and this may be the only reason he's watching over her. He's immortal and the only way to get rid of his curse is to kill one thousand evil men, to make up for the 100 good ones that he killed.
When her parents were killed on her 14th birthday, Rin swore she'd get revenge. For 2 years she practiced in her DoJo intent on bringing her parents murderer Anotsu his death. One day while visiting her fathers grave, she was spotted by old Yaobikuni. Rin told her that she intended on finding her father's (she didn't know of her mothers death at the time) murderers and killing every single one of them. Yaobikuni laughed at her and suggested she get a bodyguard. Manji finally agreed to join her and they've been together ever since. Her weapon of choice are her "Golden Wasps", daggers that she throws at her opponents. Although she trained for 2 years, she is still very much the ammateur and needs much more practicing until she can properly defend herself. She has a slight crush on Manji.
He and his men were the ones that attacked the Mutenichi-Ryu DoJo. His grandfather was denied the right to be a student in the Mutenichi-Ryu school because when his master was attacked, he used the two hand fighting style, and a foreign sword. On his deathbed, Kagehisas' father told him "to show those fools the power of our sword". Seeking to destroy every sword school in Japan and then unify them under the control of the Itto-Ryu, he started off by destroying the Mutenichi-Ryu school. Under his command Kuroi Sabato disposed of Rin's father. He allowed his men to do whatever he wish with O-Toki, Rin's mother but spared Rin, because "assaulting children, shows no class". He is a highly skilled warrior, and the man Rin must kill to avenge her families death.
A Geisha and a swordswoman, Makie was enlisted by Anotsu to kill Manji. A powerful fighter but always reluctant to strike the killing blow Makie fought Manji twice. The first time losing pathetically. Her mission was supposed to be to bring Anotsu Manji's head. She set out to do it the second time and she would've done it had it not been for Rin. She convinced Makie to spare his life and Makie then instructed Manji to watch over Rin always. So far as I've read, she's been the only one good enough to defeat Manji.
Yaobikuni, whose name means "the nun of 800 years" is immortal just like Manji. In fact she's the one who stuffed him full of the sacred blood worms and pointed Rin towards him. She will be immortal until she has saved the souls of all the sinners in Japan.
Machi is Manji's little sister. When she witnessed the killing of her husband by Manji, she regressed into the mental state of a child. Shido kidnapped Machi and forced Manji into a duel. Manji however wanted to give up the sword and said he wouldn't fight. Shido agreed to let Machi go but then sliced her to pieces as she ran to Manji. One (if not) the saddest moments in Blade history.
Kuroi is the man that Rin hates even more than Anotsu. He was the one that actually killed her father. For 2 years, he sent her love poems, hoping one day to once again meet with her. The day came and when his shoulders were revealed it turned out he had stuffed heads on them. One of his former wife and one of Rin's mother. His wish was to remove his former wives head and put Rin's head where hers once was, so that mother and daughter could be together again. Distraught and knowing she couldn't defeat him, she agreed to kill herself if he would follow. Sabato agreed, and Rin would've gone through with it had Manji not killed him on the spot.
A Officer, Saito was Machie's husband. Going home drunk, he was summoned by some other officers saying they were finally catching up to the man who had killed many of their men. Saito confronted Manji, telling him his name which sounded familiar to Manji but he couldn't quite place it. He only remembered who he was when it was too late and Saito was going to strike him down. Having no other choice, Manji killed him.
A Shogun Ninja, he had given up his former life to work on his "sword painting". When Rin came asking for help, he declined saying his blade wasn't good enough to avenge the death of his friend Asano. Manji didn't buy it and told him off, and Sori fessed up. He just didn't want to fight and risk dying. He did come through for Rin in the end.
One of Anotsu's followers, he thought he could take over Sabato's place as right hand man if he defeated Rin (who he thought was the one who had killed Sabato). His plan almost succeeded but his life came to an end at the hands of Sori.
Another one of Anotsu's followers, his sister was killed unjustly by a samurai. He was w/ Anotsu when they showed up at Rin's on the day of her birthday. That day all the swords were stolen, including a treasured Chinese sword. When Rin came upon him 2 years later she offered him 30 Ryo for the sword. He declined but later Manji won it from him in a fight.
An immortal like Manji himself, he asked that Manji join him so that they could bring Anotsu down. He believed that people are nothing but worms and almost killed Manji with a deadly poison. He kidnapped Rin and when Manji came looking for her, let himself be killed because after 200 years, he had accomplished nothing.