Daimajuu Gekitou Hagane no Oni

In the year 1999, a team of UN scientists in an attempt to tap into a new energy resource on a deserted island called Sansara, unknownigly open a portal to another universe, unleashing dormant biomechanical entities. Three years later, Takuya Goroza returns to the island of Sansara urged by a mysterious request by college chum Haruka Alford. Little does he know, his old friend isn't what he appears to be...

Synopsis from Anime News Network