Ootori Kikyou

The protagonist's ex-wife who divorced from him 4 years ago. They used to be a very loving couple and had sex every day, however after their divorce she changed completely and kept switching from a man to another while becoming better at sex.
At first Kikyou was planning on using Iori's office in order to get pregnant, but after learning about the protagonist working at the rival company, she started planning out her revenge on him.