"Wet Nurse") is a hentai series featuring a woman named Kyoko who, to relieve herself of the pain of her unsuckled milk after losing her infant son in a fatal car accident, takes a job as a wet nurse, but is quickly fired when it is found out that she has had an inappropriate relationship with one of her clients.
It then views in a small purgatory-like area where Marika, Touji and Shinji Sudo, one of Kyouko's former young clients are all shown.
Unfortunately, this is revealed to be a facade and kills Marika out of jealousy saying that she won't allow something like that to happen and will not let anybody let alone her own daughter to get in the way of her twisted happiness.
It's heavily implied that she's had multiple inappropriate relationships with other past clients of hers which possibly had also led to their deaths, including one by the name of Shinji Sudo who she had also killed.
We can infer that in the end that she had possibly been arrested for her crimes when the detectives were questioning her about the necklace and Touji and Marika's buried corpses.