Combining passive and potential form, natural?

Question

これから一生妹さんに食われ続けられる？

I found this sentence in an anime and it raised some questions about combining the potential and passive form. The meaning here is literal, her sister is a monster and she needs to eat humans (or blood) to survive. We're basically asking him if he can continue to get fed on for all his life (in order to make his sister live).

I thought it was clever to take advantage of the auxiliary here and I will assume that it is natural. I see from a very similar question that you can use both ことができる and える/うる to achieve a similar result. I want to look into the naturality of using such expressions, which is not covered in the answer. In my limited experience, I have never seen them, so can someone confirm if the two following sentences are valid and natural?

1. これから一生妹さんに食われることができる？
2. これから一生妹さんに食われえる (or うる)？

According to one person in this thread, the passive form with ことができる feels unnatural. Another person also mentions that うる is rarely used. Assuming those forms are unnatural, what would be the approach to express the same thing with another form?

Answer 1

食われ続けられる sounds natural because of 続ける. It turns the passive act of being eaten into something you do. You are the one who continues to be eaten. The potential form refers to your ability to do so. 食われ続けることができる would be equally acceptable.

食われることができる sounds as unnatural as 食われられる to me. As the other answer indicates, this construct is normally used with a volitional verb. By definition, it doesn’t go well with a passive form.

[得]{え／う}る as an subsidiary verb is used to talk about a general possibility, rather than someone’s ability to do something. For example, 食べ得る doesn’t mean you have the ability to eat something but something is generally edible or can be eaten (under particular circumstances). 食われ得る would mean there is a possibility of being eaten, and therefore, doesn’t seem to fit in this context. 食われ続け得る wouldn’t work for the same reason, either. Besides, the word choice of 食う, as opposed to neutral 食べる, doesn’t quite match the formality of 得る.

As for alternative ways to express this idea, I think you could say 食われることを許容できる to stress the permissibility of the situation. Or you could also say 食われてもいい to be much less formal and wordy. If you have to use a potential form (in the narrow sense of the term), 食われて（い）られる should be acceptable. This refers to the permissibility of a state, that of (continuously) being eaten.

Answer 2

I have the impression this does not answer your question (because it is more or less the same as the linked one), but in that case you should clarify your question.

Consider この本は読まれる as a more ordinary setence.

1. この本は読まれる This book is read
2. この本は読まれうる This book can be read
3. この本は読まれ続ける This book continues to be read
4. この本は読まれ続けられる This book can continue to be read

As alternatives to 2, (2-1) この本は読まれられる and (2-2) この本は読まれることができる are theoretically possible, but (2-1) is barely acceptable (or maybe not), and (2-2) is rather unnatural.

As alternatives to 4, (4-1) この本は読まれ続けうる and (4-2)この本は読まれ続けることができる. Again (4-1) barely acceptable and (4-2) unnatural.

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Choosing (ら)れる and うる could be a personal taste. As for the use of ことができる, however, there is one thing to consider: the subject is animate.

I found this.

「Vこと」に使える動詞は意志動詞に限られます。以下のような無意志動詞は使えません。

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As for the sentence of you question,

• これから一生妹さんに食われることができる？

would be the right one, because I guess the intended meaning is Are you willing to be eaten by your sister for the rest of your life?. Using られる/うる here would sound like asking logical possibility of being eaten.

But note that all the sentences above are not equally natural, even if they are acceptable (at least to most native speakers). Just like in English, not all sentences sound natural in passive (e.g. I have a cat cannot really be passive, right?).