In many real-time/strategy/hack-and-slash/fighting genres of games(sometimes even series), SP are classified as the character's capability and the calculable value of their energy. SP is the one of the common abbreviation of most stats, it means 'Stamina Point'.
In the series, all characters and even monsters will start off with their max SP within the level of 1-10 with 100 SP.
The Max SP refer to the maximum value or quota that the character's ability to perform any sort of actions. Which means, the higher one's Max SP is, the more and efficient variety of actions may be used.
Every resurrection or revival of characters after the Soulify effect have the minimum HP comeback value of 50% of the unit's Max SP(instead). The higher the character's level, the higher the minimum value becomes. Note that after the unit have been revived, they cannot be damaged by special attacks for several seconds.
Quite differently with MP, SP uses are at any actions, the longer the action is used, the more SP is consumed during the time.
SP, in conjunction with MP, both may regenerates at any time. SP regeneration are better if the character have better Latency and Speed. SP have faster regeneration than MP, it's speed are three times faster.
SP growth ranges a bit differently than other basic stats. Each growth varies by factors. They ranges via grades and class:
S = x1.80
A = x1.60
B = x1.55
C = x1.50
D = x1.45
E = x1.40
F = x1.35
G = x1.20