Reideen (2007)

Synopsis

Saiga is a normal high school student with a gift in mathematics. His daily routine is disrupted when his family gets news that his Father's remains have been discovered—a noted archeologist and researcher who had gone missing while exploring a site many years before. Among his remains were notes and artifacts that needed to be identified by the family near a notable triangular mountain in Japan known as "Japan's pyramid", a place suspected by some to be man-made. A meteor containing a strange robotic lifeform falls from the sky and begins to cause destruction, putting Saiga in danger and causing a mysterious bracelet from his father's research to activate and merge him with an ancient robot burried within the pyramid—a robot the runes describe as Reideen. It is now up to Saiga and guardian Reideen to fight against this unknown alien threat from the sky.

(Source: ANN)
Junki blacks out while in the ruins and witnesses a strange vision. Upon waking, he finds a gold bracelet left beside him with an inscription that reads, `The Great Reideen...`
At the same time, a meteor falls from the sky and a large mechanical beast appears out of a lake.What is this gold shining object that appeared from out of Mt. Kurokami as if in response to the mechanical beast? The story illustrates Junki`s transference between his normal life during the day and his strange life of fighting by night, the embarrassment of peers, conflict, and human drama in detail.Will the great power that Junki happened to obtain bring him glory... or fear?
*This is a remake of the 1975 series Yusha Reideen.