Opening of Eclipse! is an event that takes place during the Grand Magic Games arc.
In an attempt to escape from Mercurius, Natsu and the others run into Fiore's Army. Despite initially having the upper hand, with the arrival of Garou Knights, they begin to be overwhelmed by the great number of the soldiers. However, much to their surprise, the soldiers are suddenly swept away by a shadow, and in front of them, a shadowy figure appears that is later introduced as Rogue from the future.
Rogue tells the Fairy Tail Mages that he arrived to this time in order to make sure that the Eclipse Gate opens. He then explains that there are two ways of using the Eclipse, one being time travelling and the second one as a weapon in the form of a cannon. Even though the Mages are overjoyed with the thought of possible defeat of the Dragons, Rogue tells them that someone will get in a way of opening the Eclipse Gate, and after exclaiming that it's Lucy Heartfilia, he attacks her. However, Lucy gets shielded by her future self who takes the hit. She tells them that she didn't close the Gate and much to everyone's sadness, before taking her last breath, she tells them to protect the future. Even though Rogue is surprised by the fact that Future Lucy doesn't remember closing the Eclipse Gate, he keeps claiming that it will happen in any case. However, he is then attacked by Natsu who promises to protect Lucy's future.
The Fire Dragon Slayer then tells Lucy and the rest to leave the place. After doing so, they find themselves at the Eclipse Gate's location, just as Hisui E. Fiore begins the firing sequence. When they are revealed by Arcadios, Lucy and others join everyone else present near the Eclipse Gate before its opening begins.
As the soldiers of Fiore's Army express their happiness that the Gate is finally opening, Lucy watches in awe. While Happy and Panther Lily notice the great amount of Magic Power, Wendy and Carla state that with this, they might be able to defeat the Dragons and save the future. Even though Lucy initially agrees, she then suddenly moves forward and claims that they mustn't open the door, stating that she will close it.
While everyone else is surprised and questions Lucy's motive, Lucy keeps insisting on her words and asks them one more time to close the Eclipse Gate. Hisui argues that they can't do that as it is their weapon against the Dragons, however, Lucy claims that there's no cannon because Eclipse is a door that is connected to 400 years ago. Suddenly, everyone feels a huge tremor and then witnesses a Dragon coming out from the Gate. The Dragon roars and causes a huge destruction. While Hisui watches in shock as more Dragons come out, Lucy takes action and attempts to close the door. Crying, Hisui realizes that ten thousand Dragons are coming through the Eclipse. When Wendy questions Lucy's knowledge about the Gate, she reveals that Crux has researched it. She says that it's a device that puts together Magic from the Zeref's Book and Celestial Spirit Magic to control time, but they can't control it anymore due to the current state of the Moon. While Hisui keeps blaming herself for the incoming destruction, Lucy refuses to give up and continues her attempts to close the door.
As the Dragons keep coming through the Gate, the Exceed tell Lucy to hurry up and close it while the soldiers of Fiore's Army ask Hisui to leave the place as it's dangerous. Arcadios states that Lucy's strength alone isn't enough and that's when Yukino and Mirajane appear, with the former telling Lucy to take out her golden keys in order to use the 12 Zodiac Spirits to close the Eclipse Gate. Lucy and Yukino then combine their Magic and summon all 12 Zodiac Spirits. With Lucy telling them that she's counting on them, the Spirits charge forward while surrounded by Magic Power and push both sides of the Eclipse Gate until it's successfully closed.
Even though everyone is overjoyed to see the Eclipse Gate closed, Arcadios states that it's too early to celebrate as 7 Dragons managed to get through. That's when Future Rogue appears, seemingly not happy that Lucy and Yukino interfered. However, he then states that 7 Dragons will suffice as trying to control ten thousand would be a nightmare. Hisui recognizes him as the person who told her about the future, with Arcadios stating that she was deceived by him. Not paying attention to this, Future Rogue announces that the humanity will become extinct now as the era of Dragons is about to begin. Much to everyone's surprise, the Dragons listen to Rogue when he tells them to kill the Mages in Crocus, revealing that he's using Dragon Supremacy Magic to control them. The Dragons then descend to wreak havoc, starting the battle between Mages and Dragons.