We have no access to this game's API. So we can't know exactly the damage / resistance formula.

That question has been at the back of my mind too, and I automatically assume its 50% nin 50% tai, so no matter what you increase its the same. Then again I don't know how opponent defense and resistance affects it. Or it could be total (atk stat + nin stat) vs total (def stat + resist stat) so again it didn't matter what you increase.

Actually I'm not even sure how attack, ninjutsu, defense and resistance works too. As in, the actual math for tai damage is not directly attack stat - defense stat right. If there is actually an example that explains those, please link, much thanks.

seems reasonable to think most of them are 50% and 50%, but could be there are special cases that do not follow this rule.

Maybe it can be another of ICE's tests ;)

Right now, if we asume the dmg is spread 50/50 you can look at your ninjas growth rates and see which is higher- attack or ninjutsu - and then increase mood accordingly. Keep in mind some ninjas for example could have high attack growth but most of their skillset is ninjutsu based (or vice versa). This way even if dmg is spread 50/50, because of % increasing your higher base stats you gain more stats overall. So in order to increase your dmg as much as possible, mood your ninjas to increase their best offensive stat (but also keep an eye if its actually used in their kit, not jsut a dead stat). And obviously, stack that position with both att and nin, but those are flat increases so theres no hidden trick to that. The more the better.

Tbh its all I can think of due to 0 access to math formulas.

Idk...It could also be like LOL, for example the damage being calculated like 1.28x NN + 0.74xTAI

no, no is calculated as if was two separate attacks, one full nin and one full tai.

Is something like (full guessing):

(1-DR/100)*(K*F(A/D^0.5)+(1-K)*F(N/R^0.5))

where DR = damage reduction. F is a function, very like linear, depending on the mystery or standard attack you use. K a coefficient between 0 and 1 that states how much % of nin and tai effect gets dealt (so K = 1 if the effect is full tai, K = 0 if the effect is full nin, K = 0.5, very likely, if the effect is half nin half tai. A = attack, D = defense, N = nin, R = resistance.