You are right, normally no one would sell their soul for only one day of sight, but this case is slightly different, I think. At first I was totally confused too, but at the end of chapter 7 it was pretty clear to me, as to why he only needed one day to see. So if you haven't read up till then, this might be a bit of a spoiler.
The prince's wish was expressed as his last wish. Since there was this dagger he always kept close to him, he was thinking about ending his life all along, I think. To see his beloved one and to know he was being held and caressed by him would be his last happy memory. Therefore he could die without regrets. But since it wasn't his last day yet, he couldn't see a thing.
As to why he didn't defend himself or try to run away, I guess that was because of his sense of duty and his desire to be of use to the kingdom, which only led him to be trapped even more by his psycho-father... (￣ε(#￣)Σ
I hope that helped. If not, I was still glad to be able to rattle on about at least one part of the story I was not totally confused about. (づ￣ ³￣)づ
No need to worry about spoilers, I read all the chapters posted so far.
That part just seemed to stop abruptly with no closure.
I know he said he only needed one day of sight, but even that I thought was illogical since the demon was basically telling him "you could spend the rest of your life looking at your beloved doofus".
Then again, maybe you're right and he was planning to kill himself all along, so it didn't matter to him either way. Based on his father abusing him that makes sense.
Maybe the author isn't done with that part of the story and I just need to be patient.
I will say the way this is pieced together you really don't know where the story is going, how long it might be or when it might end.
Although confusing in parts, I suppose that's part of its charm. The manga is definitely unique.
Thanks for sharing your thoughts; I like hearing other people's take on stories like this.
I was following the weirdness OK until the part in the middle where the blind prince was getting raped by his father who was also pimping out his double to save the kingdom before the servant who secretly loves him comes to rescue him. Then suddenly up pops the demon because the kid wants to sell his soul for just one day of sight.
Forget about everything else, no one is going to sell their soul for one day of sight if they can just get their sight back, plus after that it just kind of stops.