Is It Wrong to Try to Pick Up Girls in a Dungeon?: Sword Oratoria / Danmachi Gaiden - Lefiya's love life

Danjon ni Deai o Motomeru no wa Machigatteiru Darō ka Gaiden: Sōdo Oratoria is the full Japanese title. Each volume of the Sword Oratoria series occurs at roughly the same time as the same volume in the main series, usually with the two partially overlapping. Currently there are 10 volumes out, with 6 translated into English by Yen Press. The anime adaptation covers the first four volumes.

Lefiya is introduced in volume 1, with a very obvious crush on Aiz Wallenstein. The rest of Loki Familia is quite aware of this, often teasing her about it.

In volume 2 she meets Filvis, an elf with a dark past. Filvis doesn't want to open up to anyone, but Lefiya slowly pushes her way in.

On their way back from the 59th floor, Loki Familia is attacked by venomous monsters, and forced to camp out on the 18th floor while Bete gets more anti-venom from town. Having heard of their return, Filvis makes her way down to the dungeon out of concern for Lefiya. The two have a bit of an argument over Filvis's expression of her guilt from the loss of her former party members, but they make up quickly and take a nap while holding hands under a tree.

Lefiya's crush on Aiz gets brought up on multiple occasions in the volume, especially in regards to Aiz's interactions with Bell.

This volume mostly takes place in a nearby port called Meren. Because of this, and the fact that it's not easy for adventurers to leave Orario, Filvis does not appear in the volume.

Lefiya has a few moments with Aiz this volume, most notably when she was captured, and just before being saved, "her heart cried out desperately for the one she loved."

I'm personally rooting for Lefiya x Filvis, since the two seem to have more of a relationship than a one sided crush, and both this and the main series seem to be working to set up Aiz and Bell.