Watch:
Sealed with a Kiss - Chinese drama with indirect themes of Dominance & submission (it's an alternative lifestyle). I don't know that the producers consciously set out to make a D/s drama, but that's what it essentially became based on how the relationship between the leads manifested itself. I always say - when rec'ing this drama to others - it's a drama for mature audiences only. If you're too young, with no life experience you probably will not enjoy (or understand) this drama much. You also will not enjoy this drama if you're one of those women who don't like dominant, somewhat controlling men.
My Man - Japanese movie, about an older man having relations with ... I can't remember his relation to the female lead. I think she was related to him in some way ... uncle or something, and she's also a high school student whilst he's in his mid - to - late 40s. More than the age gap in and of itself being taboo, it was how the protagonists presented their relationship to the small fishing village that they lived in that was taboo. Japan is still quite a conservative society, despite a nefarious underbelly, but these two were so 'shameless', esp given that there was some familial relation between them. Anyway, I won't say more than that so just watch it and see for yourself.
I don't actively seek out content with taboo themes, and will even tend to avoid them if they try to push the envelope too much ..., but I have to say that is picture was stellarly made. The plot was pretty good, but what I appreciated the most was the filmmaking ... how well everything juxtaposed with each other ... the bleak cinematographic colour palette matched the bleak lives and setting of the protagonists. The best cinematic experience for me is when all elements -- both the artistic and the technical -- come together nicely to create an excellent movie. This might not matter to you as much, but trust me when I say it does enhance the experience of watching films. It's the difference between a film that's just for entertainment & a film that is both entertainment AND art.