I think most people who say Melodia is because it's an NPC that AE scrapped, not because the NPC had any true memorable moments. The only memorable moment I have of that NPC was maybe one cutscene and joining the Sanctuary from that NPC. To be honest, I think most NPCs are underrated. I think the female NPCs that show a good amount of significance story-wise are Senna and Safiria (though Safiria doesn't exactly feel like a significant NPC in the Darkovia storyline due to how the story parts are branched out). At least for Senna, she appears at the beginning (DragonSlayer Camp) and at the end (Mt. Ashfall), had some puns and Easter Eggs (Senna Bun food item, secret key to access a chest), and had a debut in one of the Battleon Invasions. You don't get much out of other NPCs.