見捨てることも厭わないアルスがあえて助ける理由。 Arus is the name. In this section of the story, Arus is trying to rescue a person from death. If I understood this line correctly he either hates giving up or doesn't mind giving up. Thanks for helping~
More exactly, from the context you gave it reads as if Arus doesn't care whether others die, but there's a reason he must save ___.
It’s like @chencking said. The あえて reinforces how unusual Arus’ action is here. Also, this is technically a sentence fragment, but Japanese allows that to show emphasis or emotion. Be careful you don't leave it a fragment in English, though, because English grammar doesn’t work the same way. Try something like: "Arus, who normally had no problem with leaving people to their fates, must have had some reason to help."