Dii (ディー) is the primary antagonist of Utawarerumono. His true identity is of Witsuarunemitea's darker half. He believes in creating social progress by instigating wars to eliminate weak races and lead the people to greater heights through natural selection.
Dii is cold, calculating, and ruthless. He is a master of his own and uses other people willingly in order to achieve his goals. However, he is also bound by the rules as he explains that he and Hakuoro were never meant to meet and fight because of their opposite natures. He also fulfills his end of the bargain honorably yet will willingly and mercilessly kill those that turn against him, like he did with Genjimaru. But because of Genjimaru's sacrifice, he spares Kuuya's life, as normally she would've served him and made a pact but that was made with her predecessor.
Dii was once a noble scholar of the Onkamiyamukai. Before the events of the series, he wandered inside the cave where Witsuarunemitea's soul was sealed. It was then that the darker half was released and possessed him.
Dii is revealed to have aligned with several nations in order to achieve his goals. The most notable being Shikeripechim and Kunnekamun. He told Niwe of Hakuoro's true identity, thus making Shikeripechim declare war and provided the Avu-Kamuu to Kunnekamun so as to fight against the countries that oppressed them and enter into a pact to be his people. He also deceived Orikakan with sorcery for Kucca Kecca to declare war on Tuskuru as per Niwe's plan. In the end, Dii lost the fight and, bound by the rules, intended to sleep until he awakens once more despite having an urge to fight Hakuoro. Hakuoro, however, decides to fight Dii and the two engage in their god forms. Dii nearly won but Hakuoro decided to fuse the two halves of Witsuarunemitea together before sealing himself away so as to prevent interference from the god.
Genjimaru - Dii regarded Genjimaru as his only friend as he did not wish to lose him when he turned his blade against him. Even then, Dii held no emotion as he mercilessly killed him.
- In the visual novel, Urutorii reveals that Dii was once her teacher until his disappearance.