MC should really go to a hospital and get a blood sample drawn. That way when he sues her ass, he has clear evidence to back it up. Im no expert on Japan's legal system, but if this was in the US, she is looking at a good couple of years in prison for her employees and at minimum a juvenile detention facility until she becomes an adult which then would mover her to prison for kidnapping, drugging, sexual harassment with attempted sexual assult. Not to mention it being for a business purposes, which means it violates numerous laws for work place harassment.
But this is not the US, this is "Manga World Japan" where this kind of stuff is just takes as your average Tuesday. Many would even say he is at fault for not having sex with the underaged girl and deserved to be drugged and kidnapped.
The girl will become a reoccurring side character who continues to do these kind of things to MC to no avail. Maybe even will join the FMC's production team. Ultimately to either be left behind for the main couple's relationship to progress, or get devolved into an open ended harem which ends with either the ax, or the "why wont this just end" bullshit.