Not sure if she's reported already as a Mary Sue, but
Haruhi Suzumiya definitely qualifies.
I would even call her The Ultimate Mary Sue.
For those who never heard of her.
She's a girl who has the God-like power that what she unconsiously believes can become reality and thus can alter the world or time.
Examples. When she believes that the Sakura threes should bloom.
And suddenly the weather changes in a way that makes all the cherry blossom threes bloom.
Or when she doesn't want the summer vacation to end, and then time itself is reset on the day before school starts.
The world had to redo the same 2 weeks of summer 15,532 times !!! (but only 8 episodes full of deja-vu)
She's good at almost anything she does.
But what makes her a Mary Sue is that the story is completely centered around her.
The other characters try to keep her entertained to keep the world safe.
With the catch that she must never be made aware of her powers.
The believers of the
Haruhiism religion might see it different though.
True colours always shine brighter within darkness. ~ WonderDrow ~