Gena Isaacs is the natural daughter of the man who adopted Ivan Isaacs. Gena eventually falls in love with Ivan despite being his adoptive sister, but is killed by those influenced by Temozarela.

The natural daughter of Mister Isaacs, a ranch owner who adopted Ivan, Gena's mother died when she was very young and her father decided to adopt to keep her company. After they arrive at the ranch, Gena was excited to have a sibling until she finds out that Ivan is a boy. She promptly kicks Ivan in the shin before running away, and constantly antagonises him. After she almost gets him in trouble during dinner and is punished, Ivan visits her and gives her some of the dessert she was denied. In exchange, Ivan asks her to tell him about her mother, since he never knew his. Their friendship beings at this point.

Ivan himself is unsure of when he fell in love with Gena, but during their teenage years they develop feelings for one another even after discovering that it's forbidden. Gena helped Ivan train Jupiter, Ivan's future horse from Belial, and was deeply in love with him. However, when her father found out, he sent Ivan off to a seminary to keep them apart. Just before he left, Gena told him that "[she] won't ever be happy until [he] returns."

A few years later, Ivan returns from the seminary to find Gena waiting for him. By this time, Mister Isaacs is dead and Gena has inherited the ranch. She asks Ivan if he detests their father and he says no, saying he understood why it couldn't have been easy for him. Gena admits she did and has been waiting for him all this time, even keeping his library exactly the way it was before he left.

However, during this time Ivan gets a visit by the Order of St. Vertinez and Gena feels shunned by him. When he gets hired to open the Domas Porada, Gena asks for him to decide between her and the Order, and he chooses the Rrder. Later she is chosen as a sacrifice for Temozarela when Ivan has cracked the Domas Porada puzzle. She is used by the Order of St. Vertinez to make Ivan finally snap and release Temozarela. It is revealed they did this by sending Father Pietro to tell Gena that Ivan wanted to return to her and stay with Gena forever. She is killed while calling Ivan's name and it is revealed that one day, while she was out with Ivan, Gena asked him to be the final person she saw since she believed when people die their last image remains with them forever. Gena dies in Isaac's arms.

After Isaac sells his soul to Belial, he takes Gena's body and brings her back to the ranch with all the servants and horses killed. He dresses her in a dress and laments over her. However, Belial appears and he leaves her to talk with him. At this time, an unknown figure, possibly a servant of Temozarela, appears and raises the dead of a nearby graveyard. Ivan sees them and runs back to the house back to Gena. There, he finds several zombies feeding on her, and he snaps once more.

Ivan carves up the zombies with a scythe but before he finishes them off, Gena comes back to life as a zombie. She pleads with him to love her still, but he refuses and instead stabs her with the scythe. Gena keeps on asking why as Ivan decapitates her with the scythe finally ending her life. When he finishes killing the zombies, he takes her corpse and buries her in a makeshift grave with a cross at the head and leaves.

Gena later appears as Ivan is about to be killed by Achmode. Ivan finally begins to accept death and we see Gena in a field in front of him, before Armandiel saves him. She also appeared as a hallucination to Lizzie, saying nothing and just touching her heart, covered in blood, after Lizzie almost gave in to Temozarela.