Demon of Steel: Battle of the Great Demon Beasts

"Demon of Steel: Battle of the Great Demon Beasts" (also known as "Daimajuu Gekitou: Hagane no Oni") is a 1987 Japanese original video animation (OVA) produced by AIC. The story is set in 1999, when UN scientists on the deserted island of Samsara accidentally open a portal to another dimension while attempting to tap into a new energy resource, unleashing dormant biomechanical entities. Three years later, the protagonist, Takuya Goroza, returns to Samsara at the mysterious request of his college friend Haruka Alford, unaware that his old friend is not who he once was. Takuya discovers that Haruka's research led to a dimensional transfer and summoned a huge demonic creature called Ika Oni. To stop the chaos, Takuya pilots Hagane, another giant demonic creature from the ocean, to fight Ika Oni. The battle destroys the island, leaving Takuya floating among the wreckage. The anime is known for its biomechanical designs and fast-paced action scenes. While the pacing is somewhat slow, the final battle remains memorable.