Vigor
By sacrificing one thousand points of SP every day and only once per day, it gives you the power to increase your max SP by one point.
Luke learned the skill and immediately tried it. As expected, it was tiresome to sacrifice his SP, but it wasn't as bad as sacrificing his HP. Not even close… in any case, Luke still had a lot of coins to spend, even though he could only buy tier seven skill books and below. He wondered why he didn't find other skills like Water Manipulation. Having the power to change the environment was useful. Still, it was even more useful than increasing his parameters without leveling up? He wasn't so sure about that… Regardless, once he has some spare gold coins, he will probably get it.