I am looking for a manga that the main girl who is super strong but act weak.

Ore-sama Teacher
Kuroshitsuji - though she's not really the main character, and it's revealed just recently

Maybe Zippy Ziggy http://www.mangaupdates.com/series.html?id=9717

"...that ain't no unicorn" - Wakusei no Samidare

i read them before anymore??

Note sure if you've read this before, and your mileage may vary, but Sharon Rainsworth in Pandora Hearts seems all calm and ladylike but ends up being pretty hardcore when she needs to be. However, she is not the main character.

Also not a main character, Beni from Amatsuki seems like the perfect lady but is actually... horrifyingly capable... if you read long enough.

In a way, Dokuhime works. Emotionally, she seems frail, but obviously she's extremely deadly for reasons related to the premise of the story.

That's all I can think of right now...

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[img]http://i45.tinypic.com/mlkqj5.png[/img]

maybe Otokomae! Beads Club and Superior in a way

[img]https://c1.staticflickr.com/1/753/22668593615_519ce54b81_o.png[/img]

Katanagatari - not the main girl, but the second main girl.

Onani Master Kurosawa

Superior

Durarara!! (Novel) - a lot of these types in here, actually.

A Night of a Thousand Dreams - if you're fine that it's a girly guy. XD

thx for it^^ Speaking of Superior. is there anything similar to that manga too?

Witch Craft Works

Yankee-kun to Megane-chan - Main girl is strong but she hides behind nerdy pretense. Epic manga (hilarious).
Oresama Teacher - lol summary says it all.

A stretch would be Superior and Kuroshitsuji.

Forever lurking...

If you don't mind manhwa,
Her True Color

Obsessed with reincarnation
....
Key to the Stars

Gokusen