Keychain | Berserk | Crimson Beherit

The Crimson Beherit (真紅のベヘリット), also known as the "Egg of the King" (覇王の卵), is said to grant one the world in exchange for the owner's flesh and blood, only falling into the hands of those bearing the requisite qualities to become a member of the God Hand. Once every 216 years, during the Eclipse, an owner of the Crimson Beherit is granted an audience with the God Hand. As preordained by causality, an owner will offer a precious sacrifice in exchange for being reborn as a member of the God Hand.
(from Fandom Berserk Wiki)

Berserk
Author Kentaro Miura's classic seinen manga series Berserk is an iconic work of dark fantasy, complete with ferocious medieval-style battle scenes, terrifying supernatural monsters, magic spells, and various arcane symbols and rituals. A major example is the Brand of Sacrifice, a Berserk symbol that the antihero Guts bears on his neck. As a character, Guts is riddled with symbolic meaning and themes, such as his dragonslayer sword embodying his self-destructive desire for violent revenge. Meanwhile, his Brand of Sacrifice is a constant reminder that he is marked for doom—that Berserk's most powerful villains will stop at nothing to claim his body and soul for their own dark purposes.
(from Comic Book Resources - cbr dot com)