"Nakajima Kei is a prominent character in the manga series ""19th End Century Memorandum"". She is one of the main protagonists in the story and is known for her intelligence, leadership skills, and dedication to her work.

Kei is introduced as a member of the Bureau of Investigation, where she works alongside her colleague and friend, Takayanagi Aiko. Kei's expertise in the field of science and technology makes her an invaluable member of the Bureau and she is often tasked with deciphering complex codes and solving mysterious cases.

Throughout the series, Kei displays strong leadership qualities and an unwavering commitment to justice. She is fiercely independent and believes in taking matters into her own hands when necessary. Kei is not afraid to challenge authority and is often at odds with her superiors when she feels that their actions are unjust.

As the story progresses, Kei's character becomes more complex. She is haunted by her past and struggling to come to terms with the traumas she has experienced. Despite her inner turmoil, Kei remains determined to protect those around her and fight for what she believes in.

One of Kei's defining traits is her loyalty to her friends and colleagues. She forms close bonds with her fellow Bureau members, including Takayanagi Aiko and the enigmatic detective, Akama Shunsuke. Kei's unwavering loyalty is tested throughout the series as she is forced to make difficult choices that could potentially harm those she cares about.

In summary, Nakajima Kei is a complex and compelling character in ""19th End Century Memorandum"". Her intelligence, leadership skills, and commitment to justice make her a valuable member of the Bureau of Investigation. Her loyalty to her friends and colleagues is unwavering and her inner struggles add depth and nuance to her character."