Thanos

"This thing cannot be allowed to live. It has to be killed! Why didn't we realize it sooner?! It's too late now... We are already connected... No, I think we can break that bond between us somehow... There's got to be a way! I wanna get rid of him... as soon as I can!"

-- Oswald Leingold (referring to Thanos; timeline-wise occurs before ROT, but is shown in RotA)

"A fragment of another soul - that's what an Other Self is. A shadow of an existence, that's why Other Selves appear. Why and how we exist are still mysteries, not wanting to be solved. The harder the light, the greater the shadow... Why should I be born in that time, when his heart differed so greatly from now? Why am I not part of his soul anymore? What am I? Tell me what I actually am!"

-- Thanos, Requiem of the Abyss.

Background
Thanos is Oswald's Other Self, who was created due to Oswald's disappointment in his own abilities, as well as his dark hopes and ambitions. Being an Other Self, Thanos shares the same fate as Oswald, meaning that if Oswald dies, he will also die, and vice versa. He was an empty being and acted like a psychotic child in ROT. He did not understand the meaning of life and lived eating souls from the cycle, resulting the world's instability. He also planned to take over Oswalds's body sometime later. In ROtA, Thanos managed to obtain Oswald's essence and form his own body. He believed that his existence was purely destructive and meaningless, and even Oswald wishes for his death. As a result, Thanos took over Oswald's Realm and built a demon army for himself, and managed to take a further step in Oswald's abandoned plan to take over the world.

Appearance
Thanos has green hair, which appears brown in the Realm due to its contrasting reddish tint. He wears a cloak and his eyes are of a darker crimson as compared to Oswald's. Thanos' hair colour is as such because of the fact that Oswald's rival Aldius Tetraheilm also has the same shade of green hair.

Personality
In Requiem of the Abyss, Thanos despised everything in the world, including himself. And he took no pride in his existence, but also wanted to take everything down with him before that. As an individual, he possesses the same liking for teasing as Oswald, but he is a lot calmer, more calculative and is also a lot more thoughtful than Oswald. He is not perverted like Oswald is, and seems to be quite distant from other people. Unlike Oswald, Thanos never curses, and instead likes to make use of subtle sarcasm as well as well-mannered insults.

Relationship With Other Characters
Cheryl Leingold : Thanos was planning to use Cheryl as a tool to take over the Realm, and in his ending in ROT (which is not canon), Thanos manages to trap Oswald and return her to her own world and even revives her family as thanks. At the beginning of RotA, Cheryl considers Thanos an unforgivable threat, but changes that way of thinking later. He thinks of her as an older sister later on, but never truly respects her.

Valencia Athanae Leingold : As she possesses the same element, Thanos could relate to her a little. But Valen goes against him, and thus it left him no choice but to kill her. She was also the one who showed him how he could treasure his own existence, which left a great impact on his future.

Oswald Leingold : Oswald and Thanos were similar, and because of that, Oswald was afraid that Thanos might overpower him someday. He tried to kill him in RotA, and was almost close to succeeding. He is Oswald's mirror and even though they are basically the same person, Thanos and Oswald never get along. By the end of RotA, Thanos has returned to Oswald's body and waited to be reborn once again.

Lenarche Seleniarius : Thanos and Lenarche form the official pairing of Fantasia: MOGF. There is not yet any explanation about their relationship as the game is not yet released.

Shea : Thanos and Shea had a mutual master-underling relationship. While Thanos gave him a reason to live, he provided him help and support during ROTA timeline. Their relationship in MOGF is unknown.

Abilities
Thanos' main ability is the soul eating ability. Other than that, he also used swords in ROTA against Nazim and Klavios in their respective paths. His main weapon in MOGF is a scythe.

Fantasia - Realm of Thanos
Thanos is a minor character in Fantasia : the Realm of Thanos even though his name is used in the title.

Fantasia - Requiem of the Abyss
Thanos is the main villain in Fantasia : Requiem of the Abyss.

Fantasia - Momento of Grand Finale
In the Momento of Grand Finale Demo, Thanos is shown to find an interest in Lenarche Seleniarius due to her abilities, and met her while cloaked in a tavern. During their conversation, Thanos is still shown to be an individual who is remorseless when dealing with human lives, much to the shock of Lenarche. He also appears to be rather sinister as well as calculative and planning, and manipulative to some extent. He is suspicious of Helberg Vanguardion, and requests for Len to watch his movements as he is unable to enter the Guild himself due to the barrier present.

Thanos is the rebel leader in Fantasia - Momento of Grand Finale.