Sort of the GetBackers' closest friend, Natsumi is very devoted to Ban and Ginji, often worrying about their welfare and staying up late at the Honky Tonk to welcome them back from a mission (this is also seen in the MV of the first ending theme in the anime, although the duo were just away to get groceries on a rainy day. Also, the song is sung by Otoha, Natsumi's seiyu). In a case of real life mirroring art, in the anime, Natsumi once teamed up with Emishi on a retrieval mission (the same episode where she wore the outfit mentioned below); her seiyu (Otoha) later married a comedian. Also, she has occasionally displayed maturity beyond her age (probably an influence from Paul)
Natsumi's history and character is markedly different from the anime's. Aside from hints that she and Ginji share an almost flirtatious friendship, she was introduce as one of the GetBackers' first clients. The daughter of an eminent virus researcher, Natsumi hires them to rescue her "genius" Miniature Dachshund Lucky from performing tricks at a TV station. But Lucky, apparently, has more sinister powers and mysteries under his fur and it's up to the GetBackers to get to the bottom of what turns out to be a conspiracy involving superhuman mutants, mad scientists, and Hevn - who also makes her first appearance in the series in this arc (chronologically speaking).
Get Back the Lost Time
As their "master" battles in Infinity Fortress, Rena worried about his safety. Natsumi, however, was convinced that Paul would be alright, and told her colleague not to worry.
She has amazing ping-pong skills and even once takes on a job meant for the Get Backers, while they are busy with another case (despite her lack of skill at anything besides table tennis, shogi, and cooking. Notable here is that she chose to wear an outfit consisting of Ban's shirt and glasses, and Ginji's pants and gloves for the case).