@Kurzaa said in The Reincarnated Mastermind: Sundering Fate with Magic Swords Vol. 3 Discussion!:
In volume 2, Fiona was falling in love with someone she never met just because he stumbled across a rare material needed to save her life. Then she ended up superimposing those feelings onto a random adventurer because they had a magical static shot when they touched each other by accident. Sure, it was the same guy, but she didn't necessarily know that, she was in love with the idea of being in love and finally free to live her life.
She found out that "Mr. Adventurer" was Ren pretty quickly. He managed to give it away only a couple days into his time at the fortress thanks to him saying something about her medicine having used monster parts, and she then proceeded to verify it with someone else behind the scenes (she just didn't admit that to him until later). So, most of the time she was interacting with him, she knew exactly who he was even though she continued to call him "Mr. Adventurer."
So, she went from wanting to thank the guy who had gotten the monster part which saved her life (and who had done other amazing things that her father's butler would have told her about), to wondering if "Mr. Adventurer" might be him, to fairly quickly knowing that it was him, and then after she'd gotten to know him a bit better, he proceeded to save her several times - including from a legendary dragon. Whatever her initial feelings were and how much she knew about him, by the end of that, it would be pretty normal for her to have fallen for him.
So, I think that it's seriously selling her short to say that she was in love with the idea of love. And whether there is any truth to that read of things initially, she quickly had every reason to fall for the guy for real after having actually met him. By the time that Licia meets her in the third book, it makes perfect sense that Fiona would have genuine feelings for the guy and be determined to pursue him.