I would recommend translating key words into Japanese: most JAV have long titles/descriptions, so searching in Japanese is often the best way (in English, the description might be dropped on the site). It's the problem of finding the right words, of course, but still, that's what I would do. Knowing specific terms helps a lot. For example, one video that I love coming back to is
this one I shared in another thread
To find it, one could try and search for words like 当てる ("guess" in this context), 母、息子、父 (mother, son, dad), ゲーム etc. (and there are other great titles that can be found like that, e.g.
VOSS-031 or
RCTD-422), but knowing the specific term 人狼ゲーム ("werewolf game") is what helps to find it quicker and more precisely
The moral of the story is that I would find the keywords in your case. My guess would be that they are:
- 義父 (though it can mean "foster father" and "stepfather" as well: literally, it's like "duty father", i.e. father that is not by blood but by law generally*)
- DV, I guess, would stay the same, but one could also use 家庭内暴力 (literally "domestic violence") or simply 暴力 ("violence") to not be too specific; also, to express that it's the husband who is violent to the wife, you could specify 夫 and 妻 (husband, wife), but maybe in this context, it would be from the point of view of the father, so 息子 and 嫁 (son and daughter-in-law) and just 娘 (girl) to, again, not be too specific
- Another important part of your description is forcing her to do it, which is 強制 in this case
- And, as I understand, the relationships between in-laws could still be called 近親相姦 to make it sound more "forbidden"
Overall, I would search for these first: 嫁 娘 息子 義父 DV 暴力 強制 近親相姦 AV
(All together, they don't seem to give any specific titles, so maybe removing one or two, trying different combinations)
Once you find something which looks close, you can look for more keywords, and thus narrow down your search
Or maybe you'll find that some words are not used in JAV titles at all (maybe for legal reasons, like they don't use JK any more, as far as I know)
So, it will be a process of trial and error, adding and removing keywords, which could lead you to what you're looking for, but it's not guaranteed
P.S.
Another important part is the powerlessness in stopping the violence; this is a tricky one, in my opinion, as it can be translated in multiple ways, while being possibly one of the most important keywords here. The easiest way, I think, is to use 助けられなくて (which is a way to translate "can't/couldn't help" while implying that it's a setup for further actions, i.e. "not being able to help, I...")
* Basically, you're specifying what you mean by 義理 in this case by providing 息子 and 嫁: lots, if not all, of the titles I've seen similar to this use 息子の嫁 (son's bride/(young) wife)
