Kindness is one of many human soul types, which is the green human soul trait.
The soul of those who possess a Kindness soul trait will be green. Humans who have this soul trait usually have green eyes and green hair, for example, Mila. This isn't always the case though, Amber has a two-traited soul so her hair is blue and not green. If a determination soul becomes green, their soul won't be able to move but will be able to protect theirselves. On Glitchtale, Kindness is able to use The Shield Of Kindness as a magic weapon.
What Camila Cuevas Said About Kindness
In terms of quantity, kindness is one of the rarest traits.
This can be concluded because of the cruel human nature that humans possess. While all humans posses kindness, very few will decide to practice it and live by it with enough will power to make it their trait.
Kindness wizards, while very rare, are extremely powerful. Their defensive and healing magic is unique and very well received among their allies.
Ironically, as powerful as it is, the wizard itself is quite vulnerable when confronting an enemy. Due to their soft heart, a kindness wizard in combat, is more likely to get killed by their enemies.