100 Heroic Grails are initially needed to summon a Hero. Afterwards, the cost for summoning increases by 50 until it reaches 500, after which it remains at 500 for the rest of the available summons. Every Hero can be summoned up to a maximum of 20 times each.
200 Heroic Grails can be obtained from First Visit Bonus: Heroic Grails, by entering the Use Heroic Grails menu for the first time.