Musashi Number 9

is a manga series by Miyuki Takahashi published from April 15, 1996 to February 6, 2007 in Akita Shoten's shōjo magazine Mystery Bonita. It was collected into 21 tankōbon volumes. It spawned several sequel series published in Mystery Bonita: from April 6, 2007 to April 6, 2010 (collected into 8 tankōbon volumes), from October 6, 2010 to November 6, 2014 (collected into 12 tankōbon volumes),  from March 6, 2015 to December 6, 2019 (collected into 15 tankōbon volumes),, and  which is ongoing from January 6, 2020 (collected into 8 tankōbon volumes as of July 14, 2022).

Plot
At the 2nd book Kou's new mission is to protect Shingo Tachibana. Shingo's best friend was a photographer and accidentally took a picture of a sniper shooting someone from the top of a building. His best friend was murdered, but never revealed where the picture was hidden. Lonton (the sniper working for the Chinese Triads who'd killed Shingo's best friend) is now after Shingo, thinking he knows where the picture is located. In the end Shingo and Kou take out Lonton and he is sent to prison.

Kou stays with Shingo for the next few books, and not soon after Shingo begins to fall in love with Kou. Kou tries to remain emotionless and focus on the mission at hand, to protect Shingo), but she too is falling for him. Shingo goes through a lot trying to tell Kou he loves her; the first time her told her was when a car had just hit him and he was dazed. She heard him, but instead pretended that it was her double and that in his daze he couldn't recognize the difference between 19 (her male double) and her. She pretend she never heard, and Shingo remains quiet about it, thinking of a better way to tell her.