Apos, the primary antagonist and the fiend behind Rin and Mimi's tortured existence, is an eternal being obsessed with sacrificing Rin to Yggdrasil; the tree of all life. Apos lurks in the shadows; eager to tear into her ripe body and devour the memories of her countless lives, while Rin struggles to unravel the secrets of her endless agony.
Apos is an intersex individual - possessing both male and female sex organs - who possesses the qualities of both an Angel and an Immortal. This, according to him, makes him a "God". He seems to have no concept of human morals and instead has an incredibly sadistic nature as shown by the amount of Immortals he keeps bound and tortured because he believes their suffering and agony makes their Life Fruit taste better.
It is also revealed that he has the ability to instantly remove the fruits from both immortals and angels, thus killing them. Anyone else wishing to kill an immortal must physically dig through their victim's flesh for the Time Fruit.
In Episode Three, he reveals that he is after Rin's Time Fruit. In episode six, Apos is revealed to be the child of Tajimamori, the previous Guardian of Yggdragsil, and the current Guardian himself. Guardians are supposed to switch every once in a (long) while, but Apos desires to become a permanent guardian by sacrificing Rin to Yggdrasil.