Kumori wears a long black robe and black cape with a big mantle a big black cowl, or hood, that kept her face hidden from view—the same as Cowl.
Differently from the other power-hungry necromancers, Kumori was polite to Harry Dresden, advising Cowl that he should say please when asking for Die Lied der Erlking. She seemed to know something of the ways of wizards, since she asked Dresden to remove his rings, something that most beings didn't notice as being significant. She used her powers to prolong the life of one of John Marcone's men who was fatally injured, long enough to get him to the hospital.
Basically nothing is known about Kumori's identity, background or personality. The only book she was named in was Dead Beat, though a cloaked figure who matched her description was seen at Bianca St. Claire's ball in Grave Peril—she has never appeared again in the series, at least with this name.
In the seriesEdit
In Dead Beat, Cowl and Kumori stop Dresden outside Bock Ordered Books demanding that he hand over his copy of Die Lied der Erlking. Dresden recognized them from Bianca St. Claire's ball. Kumori attempts to be polite to Dresden when Cowl isn't. She explains that their purpose in seeking the book is to destroy it to keep it out of the hands of the Heirs of Kemmler. She tells Dresden that the White Council's end is near. At Cook County Hospital, EMT Jason Lamar told Dresden about how Kumori brought a victim back to life on Wacker Drive.
Kumori cornered Dresden outside Shiela's apartment building. She asked for the book again and gets into a philosophical discussion about her beliefs about Necromancy. Dresden told her she's different than the other Necromancers because she went out of her way to save someone while the others are all just killers. Kumori took Bob from Karrin Murphy's home after Dresden had raised the Erlking and Cowl had Dresden held at gunpoint. 
Kumori holds Dresden at knife point, holding him prisoner while Cowl attempted the Darkhallow under Evil Bob's tutelage. After Dresden released Bob from his skull, Bob took over Sue, the zombie T-rex, and swiped a huge talon at her, causing her to release Dresden. It's uncertain whether the T-rex killed her, ate her, or she escaped.
Kumori is a Japanese word meaning cloudiness.