Basing off of this chapter, I have a really stupid theory (you dont have to take this seriously) that Miyama Yuri might be Manager's ex-wife. Maybe before they were married, the Manager's ex-wife was already working as an AV actress in order to pay a debt from the yakuza (seeing as to how Manager and his coleague are kidnapped in the end) and the entire when she was with the Manager, she wrapped her chest with bandages that make her look flat so that the Manager won't be able to figure out her job. At some point, she divorced the manager because her situation became too dangerous and did it only to save him from her situation. Then when she stopped doing AV, She must've tried escaping from the yakuza and it ended up on a car chase which ultimately ended up in car crash. Thinking that maybe she died from that crash, the yakuza left her but it turns out she ended up surviving and now she has amnesia. She's now living off as an entirely different person even with a different name.
On the other hand, she might just be related to the Manager's ex wife. ๐คทโโ