An Angel's growth was supposed to be slow.
Only the favourites of the academies would grow exponentially fast compared to the others—ordinary Angels. A large part of the reason was that mana ores and null crystals are rare in the sky and restricted.
Just like this challenge, ten legal mana ores are incredibly valuable for Angels.
Demons might laugh at the pitiful amount, but for Angels, ten mana ores are worth a life.
Gaining legal mana ores was practically impossible unless the academy held something that'd reward the students with legal mana ores, and gaining null crystals was extremely difficult as it involved killing many Star Beasts.
Thus, normal Angels are practically stagnant, unable to gain either to increase their rank.
As a Lesser Angel, it should be even harder for Kai.
