The sole survivor of an Ittō-ryū massacre at Anotsu's hand and heir to her father's sword school, the "Mutenichi-ryū". She has mediocre swordsmanship skills but an intense desire to avenge the brutal death of her family. To aid in this quest, she hires Manji as a bodyguard. It is worth noting that she kisses a sleeping Manji in the fourteenth volume and has shown on numerous occasions that she develops feelings towards him. They are as of now largely unreciprocated.

At the beginning of the series she is portrayed as somebody who is trying to act mature, but is still very childish - as the series progresses she steadily "grows up" and loses much of her naivety. Rin is constantly torn by doubt over the righteousness and validity of her mission and fears becoming a hypocrite as Anotsu claims that she is more like the Ittō-ryū, especially when he remarks that she chose to use throwing knives instead of a sword like the "Mutenichi-ryū" teaches.

Rin has three weapons, a Chinese sword named Kutoneshirika which she carries in a Toju (purse-like scabbard of sorts), a Tantō type dagger and a set of small throwing daggers named Ogunchu (Golden Wasps). Even though she is only mediocre in terms of fighting ability, Rin is still more skilled with weapons than most women of that time period and the fact that she carries a small arsenal of weapons with her makes her somewhat unique.