Kushina is the easy and cheap of the 3.I only buy 80 frags of her,4 stars her from free frags from events.It took me like 4 months,but hey,its free.With Kakuzu I got very lucky,got 50% voucher in carnival twice,so 200 frags cost me only 16k coupons.Dont have Minato yet,0 frags of him.So dont give up,play the game and save coupons,and pick free frags of ninja you want.Like Kakashi summer,i have 30 frags of him completely free,just from 2-5 frags per event here and there.

And speaking of Kakashi,he can be deadly,if you power is somehow decent.And dont need him to be 4 stars XD