My advices are:
Dont spend any seal scroll till you get the kage scrolls, dont spend any coupons for ninja fragments.. spend them for medium refines or medium threads when you need.
Find a group and spend most of your coins in group skills, later for equipment and then for 8gates..
There is a ninja who can make you slow the enemy but I guess you dont have her yet, also you cant make ninjas normal attack the same person unless its a mystery or have the same passive(attack the ninja with lower hp)