Is this a dark movie?

No it's not though it can get sad at times, I'll admit I had a tear in my eye when the second of the two tanuki that searched for the elders came back.

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They should call me Hadouken 'cause I'm down right fierce!

No, not in any way, shape, or form, that I can remember at least. It's a little on the "aw man..." side, but not "dark".

I drank seven.

I think the film's witty moments stop it from becoming too dark.