Hi guys, this will be a guide on how to efficiently spend your hard earned coins.
There are 3 things in this game you can spend coins on; strengthening, donation, or black market.

It is always worth it to spend your coins on the black market for awakening materials or ninja fragments.

The main topic of this guide will be how to effectively spend your coins for strengthening and group donations. A lot of groups pressure their players to donate as much as they can, in this guide I will break down why it isn't efficient for you to donate too much to the group. If you donate you benefit from having a stronger group and upgrading group skills, if you spend coins on strengthens you improve your equipment for your ninja but won't benefit your group. There is no right answer as to which is better to invest into, however there is an answer as to which to invest in WHEN.

As a rule of thumb I try to keep my strengthens within 3 levels of my main character, however at higher levels strengthens become extremely expensive and you will need to determine how to spend your coins for the most power. The simplest way to determine this is with basic math, for me I do this: which will get me more battler power, 300k (100 group points) coins towards donations or 300k towards strengthens? If 300k to group skills only gives me 15 battle power vs 300k to strengthens give me 20 battle power, im going to spend on the battle power. Now if 300k to both give you the same amount of power, go for the strengthens, the reason being you can get free points from group convoy and plunder and upgrade your equipment for free for the few days or how ever long strengthening is more beneficial to you, and also because the group skill shave a cool down. Lastly 300k group contributions get you 15 power and strengthens give you 2-3 then it's obvious which to go after. Personally for me when my equipment reached lvl 70 it stopped being worth it to strengthen, at all levels before 70 in my personal opinion it's better to keep your strengthens within 3-5 levels of your main character. Donating is important to groups so I would donate roughly 150k a day to the group just to contribute and get a little extra power from group skills. All in all, it isnt worth it to put yourself behind by donating too much to the group, it is important to keep a balance so your strengthens are up to par and donate to your group when you can.