My main problem is he's supposed to be an adventurer. It's not like he hasn't killed before, and with every other depiction of Adventurers in media, part of their job is also capturing bandits. So him being so adverse to killing that he lets known murderers walk away is a bit too naive to make sense
As for Nenemoa, her owner is shown to have connections to some sort of evil laboratory, so if she IS alive when he finds her, it won't be long before she's either dead, or turned into some monstrosity.