I was lost with finding the last elder scroll. I went to the college of winter hold and the librarian gave me a insane book. That later led me off to the author Setpmis Signus. I wanted to help him out mostly get the elder scroll. But when I returned from a very very long journey through Aftland to black reach... He told me he needed harvested blood. So when I went to the exit I was very surprised to see a wretched abyss... No, at first glare I just walked away and looked for another exit. (This kind of thing happens all the time, daedra are as common as wolves to me.) So then I realized that was the only way out and I talked to him. Then he demanded me to be his servant. So I denied and went on with my dawnguard quest. So later I looked up the quest and many people have had the same question. I found out working with him will turn out to be a waste of hard work to kill a powerful dragon which ends up with mora stealing the kill. But I don't wanna be his servant for the rest of entirety. So what should I do?

Um.....wut.

Discerning the Transmundane ends with reading a book as the reward. It's not related at all to the Dragonborn DLC, except that 'ol Mora's involved.

Yeah, Miraak is the one who'll nick your dragon souls, not Herma Mora and you don't have kill any dragons to harvest blood for Septimus.