Mmm, now this is what I wanted: an actually good reason for the main character to let an antagonist go free. As previously stated by the more intelligent members of the comment section above, Kufa cannot risk killing Madia as that would definitely tip off the guild that he was hiding something, something big enough to kill a fellow member of the same guild.
That aside, she is very uwu... I'm sorry, guys, but I'm still adamant on liking Melida...