I just got done reading the latest update to Akame ga Kiru! and I'm pretty mad because of...a certain event. Anyway, one of the characters, a female named Chelsea is an assassin who has almost as much as many kills as the main female does. Not because of strength though, because of subterfuge. While her teammates are engaging in flashy battles, she takes the backseat and picks off her opponents one at a time, at one point very nearly killing one of the main antagonists.

But Chelsea isn't your ruthless type (it's kind of a saving grace, because manga has very ruthless female leads to begin with), she's just extremely smart.

Are there any manga with a lead like that?

Any genre is acceptable.

Alyosha! she is lacking common sense(didnt grow in an environment that would develop it), but when it comes to killing she is very strategic.

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Few favs
Comedy:
Kyou kara ore wa!!, Mx0, Angel Densetsu, Skip Beat, Ai Kora, The Devil King is Bored

Romance:
Hana to Akuma, No bra, Shinigami Trilogy, kindan no koi de ikou, Usagi Drop, Threads of Time, Girl Friends

Most under rated:
Kindan no koi de ikou, kyou kara ore wa!.
m0r l83r... maybe >_>

One of the split personalities in Change 123 is the smart strategic fighter type

ha, thanks for the suggestions but I''ve already read both of those. >.<

I think I would really enjoy a story with a MC like that... shame they're not very popular.
If in the future they are, a search where they may appear would be: Baka-Updates Manga - Search which is only a combination of 3 categories: Strong+Smart+Fighter

Chang Ge Xing is a perfect example. She's a strategist, knows martial arts, and is very badass all while realistic in a historical China type setting.

Dark Air -The main female character, Shenandoah is pretty awesome she fights almost like a berserker.