The Gate is a portal between worlds that can be opened through the use of either demonic magic or celestial force. It is through this tear between dimensions that a person may access parallel worlds outside of their own.
As the entryway between different planes of existence, the Gate consists of a seemingly endless tunnel of swirling energy and light connecting the worlds of Ente Isla and the Earth. The Gate can only be opened through the use of magic, although sufficient magical force is required to fully control the portal and traverse the boundaries between both realities. Due to the scarcity of supernatural powers on Earth, it is much more difficult to amass the necessary power to operate the Gate for those who exist in the latter world. It appears that one must possess the ability to fly in order to navigate the interior of the portal, though the tunnel itself appears to accelerate movement. The high speed which the travelers move is capable of causing discomfort for those unused to it, with Albert suffering from motion sickness in one instance. The exact distant between Earth and Ente Isla is unknown, but the space within the void is shown to be vast, as shown when Emerada took an extended amount of time to reach the end during her search for Emilia.
It is possible for the Gate to resonate with magical energy left behind but its caster at a previous point, once such example occurring when Maou attempted to send the Archangel Sariel back to Ente Isla. Due to the portal connecting with a small spell he had cast earlier at the MgRonald's, the Gate dropped Sariel off in the restaurant's walk-in freezer, where he was discovered the next day by the staff.
Despite the Earth's scarcity of magical power, the Gate has been shown to exude supernatural energy while left open for extended periods, allowing those with supernatural abilities who are in close proximity to the portal, to absorb the magic from within and sustain themselves for a period of time on Earth. This is shown most prominently when an elite legion of 1,200 Malebranche Demons came to Japan, and were able to maintain demonic form along with the ability to fly while within range of the open Gate. During this time, Satan, Alciel, and Lucifer were able to regain their original forms and powers. The boost in power produced the portal appears to be fleeting, as the departure of the Malebranches and subsequent closing the inter-dimensional tunnel resulted in the trio returning to their human forms. The loss of power is shown to be sudden, as the three were flying over the ocean during this time and instantly fell from the sky, landing in the water below.
After his defeat at the hands of Emilia, King Satan fled through the portal alongside Alciel, swearing to one day return and conquer Ente Isla and destroying his enemies. They were subsequent pursued by Emilia, who intended to kill him for his crimes against her homeland, though the dimensional travelers were left depowered upon their arrival on Earth. The Gate was used again by Lucifer, who plotted with the High Priest Olba Meyer to kill the others before returning home. Companions of the Hero, Emeralda Etuva and Albert Ende, would later travel through the portal to find Emilia, though they return without her shortly after she decides to remain in Japan.
The Church's Inquisitor Crestia Bell later arrives through the Gate with the Archangel Sariel in a quest to eliminate the Demon King. Unbeknownst to Bell, her angelic companion truly sought the fragments of Yesod, from which Emilia's sword Better Half was crafted from. He tortures Emi in an attempt to remove Better Half from within her body, but is unable to do so and ultimately defeated with Maou appears in his full demon form to rescue Emi. After defeating the pompous archangel, the Demon King attempts to get rid of him by tossing him back through the Gate. In an odd turn of events, the portal resonates with the last bit of magic performed by its caster, instead dropping Sariel off in the freezer of the local MgRonald's restaurant.
Olba later uses the gate to return to Ente Isla, after which he deviously plots behind the scenes. His scheme results in several Malebranche Demons heading to Earth to search for answers concerning the disappearance of their leader and the Hero. They bring a legion of 1,200 warriors through the gate and appear in Japan, leaving the Gate open to sustain their demonic powers. The assault is stopped by Emilia herself, before King Satan appears with his remaining generals and orders them to stand down, forcing the legion to go back to Ente Isla to tell the Demon World that their leaders are still alive and well on Earth. Upon their departure, the Gate disappears along with the magic sustaining the demons, resulting in Maou, Urushihara, and Ashiya losing their powers once more.