Power is important, but so are ninjas. You need to balance that, because if you go all-in for power, you will lose to weaker people but with top quality teams, as well as if you go all in for ninjas, you will lose to middle-tier team with more power. My suggestion is look at the best teams for the main you want to play in the future and start piecing those ninjas (if you have any doubt, you can ask here for advice too). Ideally, you would want to spend your coupons in either lucky board or mission general mobilization events, where you get a lot of power items from board/boxes, and you can redeem some fragments of those desired ninjas (but only them, not some random ones) with points. That's the best strategy if you want to stay competitive.

At your current level/power the best option for you is lucky board. When that event appears you just use them all there.

2k on lucky board

Hello, in that level you are , i would suggest keeping them and spending them always once in a month in lucky board mostly.. Lucky board for low level and power can give you plenty of good items, plus you will redeem something from it, ninja fragments or power items such as charm material packs ( i recommend charm packs from there 100%).. if you like a ninja from the event you can get as much as you can fragments of him.. but clearly for me Lucky board for low power and level is the best event at the moment. Take in mind that you need to be smart and see the best combo that you can do with your coupons, if you are lucky and Fukurokumaru's event is on when lucky board is on, you can get rebate items from spending coupons as well. Try to balance your desires and see if you want a ninja more than power items. at this point you will need to make a good cheap formations and then go for full power.