Hardest character to defend?

[Stark]

Plot no-jutsu lol

 

[~Uzumaki~]

Hiruzen, you basically have nothing to use for his defense except 'god of shinobi'(+rep to Owari for doing it so valiantly though)
also Minato cuz people have this preconcieved notion of 'the bigger your jutsu, the stronger you are' so he's really underrated and there's the fact that every Minato defender is considered a fanboy *sigh*

 

[Bogard]

Idk, any smart character because its hard to say how they'll fight their opponent since they mostly use tactics

This^

 

[Prince Charles]

minato because he lacks feats

 

[Multiply]

ten-ten, She can't defeat anyone in battle. Not even Konohamaru.