Although he has the highest stats on global right now, he is the worst ★6 character. Why? Because of his Ninjutsu, Special and Range of course. That is all said in comparison to other ★6 units and it doesn't mean that he is bad.
He is able to kill a fodder unit with one hit , but only one at a time. It's rare that he attacks 2 or 3 enemies at once. (With max pills + 'possible' buddy skill: over 1600 Dmg).
With his Ninjutsu he is able to deal over 3000 dmg to a normal enemy. If you activate his Special his Attack rises over 2400 or 2500 (depends on buddy skill), after that you can wait and activate his Ninjustu again, but he will only deal over 4500 Dmg.
In comparison to the Special of other 6* units that is almost 50% less Dmg. That means he won't be very helpful to deal a lot of Dmg to a Boss, but you can use him and his Ninjustu to get rid of the annoying fodder units on a boss stage at first. Especially if the enemies have all weak attributes.
His Field skill is nice, it gives you a chance to do a counter attack after an enemy attacks you. But most of the time it will be used only by himself, because of his short range. Other units have to be in his range to get a 25%-50% chance to counter, what is very risky for your health.
Highest stats on global so far
Ninjutsu deals AOE Dmg with a chance on slip dmg
Low Chakra cost
Field skill gives a chance for counter attack
He has a short range
Special boosts only his own Attack
Low Ninjutsu multiplier
Thanks to VynnIce for his awesome evaluation notes!