I did some research and found out how much damage increases for extra fury. Here's the result
Formation: Rukia>Yumichika+Main(1xBasic fury stone)>Sado
Main Skill: 5th
For 100 fury skill damage= 9931
For 104 fury skill damage= 10030 Extra Damage(10030-9931)=99 Increase Each Extra Fury Point Rate=.249219615%
For 130 fury skill damage= 10676 Extra Damage(10676-9931)=745 Increase Each Extra Fury Point Rate=.2500587838%
For 134 fury skill damage= 10775 Extra Damage(10775-9931)=844 Increase Each Extra Fury Point Rate=.249960018%
So, overoll damage increase rate for each extra fury point is .25%.
nice one! i always thought the more fury is, the more damage we will dealt. sometimes i unleash skill with around 130 fury, and damage is very high too