You can recover Mana in the following ways:
① Time Passing
Every five hours, one Mana is recovered.
However, this recovery method cannot exceed the maximum.
② Recovery by using "Lodestar Gems"
You can use ten Lodestar Gems to recover one Mana.
There is no limit to how many times Mana can be recovered with Lodestar Gems, but you cannot recover Mana beyond the inventory maximum of 99.
You can also obtain Mana by accomplishing missions and exchanging at the shop.