Crossed Thanatos

Crossed Thanatos is a near-invincible monster summoned by Kilkapul. Its summoning required Kilkapul to sacrifice himself, his family, and his village. It is completely immune to both magical and physical attacks. It can split into more versions of itself when attacked.

Appearance
Crossed Thanatos looks similar to a reaper or how 'Death' is often depicted. Crossed Thanatos has a white cloak and its 'face' is simply depicted as a gray spot. Attacking Crossed Thanatos reveals that its insides are made of a grey, mist-like substance. It wields a large cross as a weapon.

Personality
Crossed Thanatos shows little to no personality, as it never said a word. Its sole objective was to kill Seiya.

History
After being summoned, Crossed Thanatos relentlessly chased down Seiya, even into the Divine Realm. It easily dispatched gods that got in its way. Having no other option, Seiya lead it to Valkyrie and gets it to destroy her painting, enraging her. It is defeated and never seen again once she used Valhalla's Gate to seal it away.

Trivia

 * Thanatos was a character from Greek mythology, and was the personification of death. This is somewhat befitting of how Crossed Thanatos acts and looks.