Opening 200 boxes hoping for tendo or hashirama is wishful thinking.
In an average server there are at least 15 active players. Lets imagine that 10 get 10 boxes a day while the other 5 only 9.
Thats a total of 145 boxes opened daily. Yet rarely if ever, do someone opens hashirama or tendo during the missions event during the week.
So after 145*7 = 1015 opened boxes its already very fortunate if someone got a ninja.
Bottom line, do not spend coupons in boxes hoping to get hashirama or tendo. Open them for their contnents (runes, magatamas) + the 10 points that you can exchange for other ninja frags or even better, medium refines! (you can get a total of 70 medium refines in a week here!).
Congratz on thos lucky bast.... i mean, lucky gentlemen :P who managed to get a ninja from the boxes. But for the rest of non rng blessed mortals it is a bad idea to spend coupons in boxes exclusively for a ninja. Mathematically it just wont happen.