Reflector Device

The is the mysterious key item of YU-NO: A Girl Who Chants Love at the Bound of this World. It allows Takuya Arima to travel between different parallel worlds, with the ultimate goal of saving all of humanity from a catastrophic event.

Functionality
The Reflector Device is what allows Takuya to travel between the different parallel worlds and dimensions as outlined in the Tree of Vrinda.
 * By clicking on one of the individual jewels on the device, it allows Takuya to lock in a certain time and place as a "save" point, which he can return to by pressing the larger jewel on the device. In the game, the player must reset the jewel after returning to that save point, while in the anime, Takuya simply has a save point there.
 * At the end of each "route", a chaos correction will occur. This simply means that Takuya has reached the end of his mission in that world and will be forcibly returned to the night after Ryuzoji threatened him with a gun. In the anime, Takuya will receive a jewel at the end of each route instead, which will activate the chaos correction and send him back promptly.
 * The purpose of the Reflector Device is to open the door to Dela Grante on Triangle Mountain. The device will activate as soon as all 10 jewels are placed on the device (8 in the anime). This will send Takuya into the past 8000 years, set in a "isekai" setting.