Genin Medal gives a 5% bonus

Chunin: 10%

Jonin: 15%

You should be able to see it beside the Will of Fire panel (Where you can spend coins/coupons to boost dmg)

I do see it, and i got Jonin one with 15% bonus, but what I do not understand is, what does that "BONUS" means...

If you have read my post you would have understood that I said that my damage to 9 tail is unchanged!

I'm not a Jonin Medal user but i'm gonna give it a shot .. I guess that 15% bonus is for the Damage bonus, but i'm not sure if that's for the whole team or for your Main Character only .. In addition with that, damage in Nine Tails Invasion is not accurate and not always the same number .. I for example, my Main Character's skill delivers 240k damage at the 1st and 2nd try, regardless of the round, and when i did my 3rd try my Main Character's skill drops down to 80k even tho the whole elements is there, the barrier and the buffs, just like the 1st and 2nd try .. then at 4th try i goes up to 180k and so on and so forth ..

Anyways, lets wait for someone who knows well how this power-up thing works in Ninetails and gives you enlightenment with your query ..

I am pretty sure the bonus is for exp/coins gained not for damage landed.