A member of a clan of wraiths who inhabit dark caves and attack passing demons to feed off them, the cave she and her clan inhabits collapses when Primtine's castle passes through. She and her clan vow revenge and attack the castle. The first Eiki was allegedly a girl who committed suicide in another world upon the death of her lover and her unquiet soul ended up in the demon realm. For this reason Eiki and her kin are uncomfortable with red ropes, strings and threads as they were supposed to be a symbol of binding love. After Fabio rapes her and she joins the castle's army, Eiki repeatedly stalks Fabio by staying in his shadow and watching him work. As this is potentially disastrous due to his handling of confidential information, Fabio tries various methods to convince her to stay away and only succeeds when he uses bondage sex with electric shock on her. Eiki's ability to inhabit shadows as well as dark and quiet places unnerves the other castle residents, giving rumours of a ghost haunting the castle. Fabio realises it will need time for the castle denizens to get used to Eiki as she doesn't attack her allies. In her end, Eiki eventually returns to her cave but feels lonely without Fabio. Once her enforced vacation ends, she plans to return to Fabio's side.