[General] If you could have one power (from anime / manga)

Ability to control time perfectly

The ability to freely manipulate probability. You can do anything at all with that.

I would have a pocket dimension to store stuff in, or the ability to time travel.

dammit, I was going to say this

but yeah, Haruhi's ability is pree coo.

Loli beam.

AT-Field, of Kaworu's level or better please.

I would have to say The Branch Of Sin that The Wretched Egg uses from Deadman Wonderland...... it would be badass to be able to regenerate from any wound yet kick ass