Descend to the tunnel with glowing crystals

You descend carefully, guided by the light of the glowing crystals.

After a few minutes, you spot a glint of metal. It's a magic sword and a suit of armor! Their surfaces are marked with runes that glow in the dim purple light of the crystals. They seem too good to be true, and the unsettling ambiance of the cave makes you feel nervous...

As you approach the artifacts, you notice a nude girl walking, her movements are slow. Her eyes are disoriented, her mouth slightly open, and she drools. She smiles and looks at you.

You try to speak to her, but she only responds, "I serve the great master. I am happy. You will be happy too."

You take the sword, and you can easily kill the creepy girl, but she's not frightened of you.

What do you do?