Reimu Hakurei is one, if not the most well known characters of the Touhou franchise. She has appeared as a playable character in almost all of the games in the series, starting from the very first one.
Reimu is the sole survivor of her clan and the only maiden at the Hakurei Shrine, the boundary between Gensokyo and the human world. She is described as being very easygoing, optimistic and sympathetic towards others. As such she gets along with even those who were once her enemies. She's naturally talented, but also a little bit lazy, which is why her spiritual powers are somewhat limited, but she does have the ability to use her Ying-Yang Orb and amulets as weapons to compensate for that. She has also developed the ability to fly on her own, earlier she had to use her turtle familiar, Genjii, to accomplish this.
As the maiden of the Hakurei Shrine her duties are to keep the residents of Gensokyo from wandering to human settlements and outsiders away from Gensokyo, as well as the maintenance of the shrine itself. Not that she's really bothered by either of those tasks.