Yukito, being the ambitious fucker he is, applies to be a domestic servant at a mansion. The landlady tells him he can only get the job if he masturbates in front of her. He gets the job.
Ayame and her sister know that their dad's been lonely ever since their mom left home. Like any good daughter, they just want their dad to be happy and help in any way possible. And we do mean, Any. Way. Possible.