The Gate ( 扉 or Tobira ) is a mysterious artifact whose existence has been disclosed in The King of Fighters XIII. It is a large portal which allows time travel to every one who crosses through it and requires large amounts of energy in order to properly function. It is controlled by Saiki, the leader of Those from the Past. The Rose Stadium was built on the location of the Gate thanks to Botan's influence over Rose. Even though the actual Gate was shown in KoF XIII the device has influenced the events of KoF 2003 and KoF XI as the attacks on the three sacred treasures and the presence of Those from the Past in this time are linked to it.
In KoF XIII's bad ending, shown if the player fails the conditions to meet Saiki, notices how his plan failed and states that he'll "rewind" everything. It was Ash Crimson the one who actually foiled their plans since he released the energy that was stored from the fighters of the tournament; thus it could be implied that the Gate's failure in the main proper story mode was due to another interference from Ash.
If the player manages to meet Saiki, Saiki orders his followers to form an energy barrier in order to power up the Gate. After fighting with the opposing team, Saiki notices that the Gate that should have been completely open has begun to close as two of the Time Spheres were empty. Ash Crimson then appears and kills Saiki, taking his flames with him, but Saiki uses Ash's body for himself, thinking that this will give the gate enough energy to remain open. Upon Evil Ash's defeat, Saiki tells Ash to cross the gate so as to repeat and rewind everything to zero, but Ash just stands before Saiki, using all of his energy to make sure the gate is closed. The gate closes and disappears, taking Saiki with it. But upon realizing the Saiki is Ash's ancestor, he also disappears dying as he shouldn't have existed in the first place without his ancestor.
If the player loses to either Saiki or Evil Ash in Story Mode, another bad ending will be triggered. The Gate opens and Saiki smirks, stating that this marks the end of the world. He also states that he has finally achieved his goal to wipe out humanity from existence, as he walks slowly to the light inside the Gate. He then speaks to the doomed inhabitants that he is going to savor this and that he got plenty of time.