Dr. Ran'Tao showed up during the Bount arc as the scientist responsible for accidentally creating the entire Bount race. She's visually identical to Yoshino Sōma except for glasses and her hair pinned up—fans often note the resemblance to Nanao Ise too—and they share the same voice actress. According to Ran'Tao herself, she's far older than she appears but has figured out how to stay young-looking; the catch is she needs about twelve hours of sleep daily to maintain it.
Wracked with guilt over creating the Bounts, she ended up caring for them and helped establish a sanctuary where they could live safely while facing persecution from regular humans. She negotiated with Soul Society to grant them protection, but when she returned to Seireitei, she was arrested immediately and tried by Center 46 for her failed experiments. Once the order came down to exterminate the Bounts as a threat, Ran'Tao snuck out to the real world and helped them escape—Jin Kariya was one of them, and she gave him his doll, Messer.
Soul Society caught up with her eventually. They sealed her shinigami powers and exiled her from Seireitei. She's been hiding out in an underground shelter in Rukongai since then, spending her time on small-scale experiments involving spiritual energy. One of her creations was a kidō shotgun, which she used against Jin Kariya when they finally faced off.
Content compiled by AnimeList.moe from publicly available sources.
