Bijuu Dama.
If it didn't have holes in it i would probably think it could tank anything in the explosive category without hurting hiruzen who is inside. But i digress. (afterall it is naruto) so why not he can tank most things since that thing is practically unbreakable.
Sai's ink could take it.
I think the weakest thing that could break it is probably Kisame's shark bullet thing.
You must be joking. Only something on the level or C0, Kirin, or a Bijuu dama are getting through something that's supposed to be harder than diamond.
OP: I think the weakest thing to get through is the 3rd Raikage's single finger nukite.
Adamantine is the hardest metal so yea it would be hard as hell to break
Stronger than this one
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