Surtr (Fate/Grand Order)

"Ahh... OPHELIA!!!"

- Surtr

Surtr is a major antagonist in Fate/Grand Order: Cosmos in the Lostbelt, serving as the primary antagonist in its second chapter, Götterdämmerung: The Eternal Ice-Flame Century, which took place in Norse Mythology. He possessed the body of Sigure, the Saber-Class Servant of Ophelia Phamrsolone, the Norse Lostbelt's Crypter. He is based on Surtur the Fire Giant from Norse Mythology.

He is voiced by Kenjiro Tsuda, who also voiced Sigurd in the same game. Outside Fate/Grand Order, Kenjiro is known for voicing Seto Kaiba from Yu-Gi-Oh! franchise.

Overview
In the timeline of the Norse Lostbelt, Sutr devoured the wolf Fenrir as an attempt against the intended events of Ragnarok, gaining immense ice power that thwarted all the gods. Instead of bringing the Twilight of the Gods as he was suppossed to, he chose to bring about the Twilight of the World. He killed many gods and the leading giants, until he was sealed inside a false Sun by Odin, who also died in the process.

However, the essence of Surtur has been secretly lurking inside the body of Sigurd, the servant of Ophelia, whom he developed a secret romantic relationship with, and he was reminded by her of his destructive capabilities and wants to burn the whole world in an effort to woo her. Though like with Napoleon, Ophelia doesn't reciprocate those feelings.

Final Battle and Defeat
During the final battle against Chaldea, Napoleon managed to wound him with his Noble Phantasm, while sacrificing himself. Napoleon's sacrifice eventually made Ophelia regained her sanity and was rescued by the Protagonist and Mash.

After overcoming her fear towards Surtr, Ophelia was moved by Napoleon's sacrifice and agreed to help Mash and the Protagonist to defeat him. She risked herself by using her hidden Mystic Eye, severing the tie between her and Surtur in progress. Ophelia's actions weakened Surtr enough for the Protagonist and his allies to land attack upon him, destroying him once and for all at the costs of the lives of Sigurd and Brynhildr. Before his death, Surtr showed his regret over not being able to understand humanity before disingtagrating.

Trivia

 * Although Surtr appeared in the trailer of Götterdämmerung chapter, there's no hint that he has such a prominent role in the said chapter, given to the fact that Ophelia and Scathach-Skadi are branded as main villains due to their status as a Crypter and a Lostbelt King, respectively.
 * There are several forshadowing that Sigurd is possessed by another powerful entity, like showing Lostbelt aspects while being a Heroic Spirit from Human History, as well as defying Ophelia's order to attack Mash at times during the battles, forcing Ophelia to weaken him with her Command Spell.
 * Surtr is the first arc villain in Cosmos in the Lostbelt who is neither a Crypter nor a Lostbelt King. He eventually overshadowed both Ophelia and Scathach-Skadi as the greatest threat to the entire Lostbelt, forcing both of them to ally with Chaledean crew to fight him off.