Spirits of Rage (info, skills, hints and etc.) *may include SPOILERS*

[Sandsai]

Originally Posted by Amamake

It can give you unit an additional turn. It's also spammable if you are lucky enough to get those -rest bonuses.

So the level ups are completely random? Meaning you can get rest bonuses from the very beginning sequential to the point of reaching only 1 or 2 turn rests?