New Heroes summoning events are held whenever new Heroes are added to the lineup. After summoning 40 times during an event, you'll be able to use the Free 5★ Summon feature to summon a focus 5★ Hero for free. Be sure to use your free first summon, as well as the First Summon Tickets you can get from Forging Bonds, to contribute toward your total number of summons! These events take place roughly once per month.
When you summon a Hero using the Free 5★ Summon feature on eligible summoning events, you'll also receive a Celestial Stone, an in-game item that can be exchanged for other in-game items in the Celestial Stone Shop. While the number of times you can exchange for items in the shop is limited, the number will reset at certain intervals.
When summoning, you can spend Orbs at a reduced rate by summoning on all five stones during a single session rather than only summoning on the colors of your choosing. You can take advantage of this to efficiently work toward the 40 summons needed to enable the Free 5★ Summon feature.