Magia Stone is one of the main currencies.
Contrary to other currencies, you can buy some with your own money.
It can be obtained by completing quests in Main Story Quests, Another Story Quests, Magical Girl Story Quests, Daily Quests, Event. He can be also a reward for Login Bonus and Missions.
Magia Stones are needed to roll Gacha Magical Girls (see Gacha rates for more information), you can use them to fulfill your AP .
There is a Shop for Magia Stone, you can exchange your Magia Stones for 
AP Potion 50 , 
AP Potion and 
Gacha Ticket.
It's recommended to buy the Pack 【10 Gacha Ticket | 1 AP Potion | 1 AP Potion 50】for 200 Magia Stones every month. In contrast, 10 rolls Gacha cost 250 Magia Stones.