"This mirror, with its mysterious light... It was made of a substance that I had never seen before. It seemed important. I decided to... borrow it for a while."
The Mirror is a special object encountered in The Last Guardian. It can be used in attacks and to help the protagonists progress.
The Mirror is about the size of a dinner plate (about 12-18 inches across) and is slightly concave towards the user. There is a handle on the inner side, as well as intricate markings, while the outside is burnished and smooth. The mirror's material is unknown, but seems like some sort of green metal like the armor of an Armored Trico, although much more shiny.
"The Lightning that flew from the beast's tail took me greatly by surprise. Could it really have been summoned by the mirror?"When equipped, the Boy can aim it at a surface or a target to cast a symbol onto it. After a short buildup, Trico's tail fires a very powerful electrical charge at the symbol's location, destroying anything it touches. This can break down doors, stone walls, and, of course, wipe out enemies.
This Mirror works whether indoors or outdoors as it seems to cast its own light. When not in use, the Mirror is slung across the Boy's back.
The Mirror seems to have some kind of connection to Trico, as he is entranced by it and it only summons lightning from his tail even if there are other Trico-beasts around. Even when many miles away, he is somehow aware of the mirror being used.
Soon after the Boy and Trico wake up in the cave, the Boy, after crawling through a small tunnel, comes across a large, misty room and picks up the Mirror from one end of the room. When Trico sees the mirror flashing, he briefly becomes briefly entranced, his eyes flashing all three colors (pink, green and, yellow). When the Boy focuses the object's light on a large door, Trico's tail blasts it to smithereens with a crackling stream of lightning. This ability comes in handy, but the Mirror is lost when Trico falls under a trance and swallows the Boy. Although he regurgitates the Boy, the Mirror is not returned.
However, after another regurgitation, the Mirror is regained and its power is put to good use destroying Knights and Talismans at long range, as it now fires a built up pulse of explosive power. When the Boy and Trico encounter the Master of the Valley on the top of the Citadel, it is the power of the Mirror that destroys the evil being once and for all.
Once the Boy is returned to his village, the Mirror disappears for a long time but is found half-buried in the dirt near the village. The Boy, now a man, shines the Mirror's light into the sky. Many miles away, back at the Nest, Trico receives the call and coos happily.