Normally, we need to use Orbs to summon Heroes, but when you summon on an event for the first time, you'll be able to summon once without spending any Orbs!
You mean we can summon for free?! Well, that certainly sounds helpful! I get the impression that our summoner's been working pretty hard to stay on top of our Orb supply.
There'll be notifications on the castle bulletin board and in the castle hall when free summons are available, so don't forget to check in.
Oh, so that's what that was all about! I had noticed banners saying "Summon for free!" in the castle hall.
Incidentally, I hear there's some kind of otherworld carrier-pigeon service called Twitter that's being used to share information about summoning new Heroes. I'm not too sure on the details for that one myself, but, uh... See what you can find out.
Get One Free Summon on New Summoning Events and Summoning Event Revivals
When summoning events take place, even if they're summoning event revivals, your first summon typically won't cost any orbs. Don't forget to take advantage of this when the opportunity presents itself! "Summon for free!" will be displayed on Home Screen notifications and banners when a free summon is available, so make sure to keep your eyes peeled.
Check the Official Twitter Account
The official Japanese and English Twitter accounts will post tweets to notify players about summoning events taking place. There'll also be tweets with news about various other events too, so why not give the accounts a follow? (Only available in Japanese and English.)