Botan is a perky guide to the Underworld. She guides people that have passed away to the Spirit World. Yusuke was among the many people she guided and once he was brought back to life she became his assistant.
Yu Yu Hakusho and all associated characters are copyright of Togashi Yoshihiro, Studio Pierrot, Fuji TV, Shounen Jump Weekly, and Shueisha. It's licensed by FUNimation Productions, Ltd. This is simply a fan site to it.