Luka knows that she scares people.
She knows that people find her antisocial nature off-putting. She knows that people find her strange because she prefers not to talk much. She knows about how people would jump in surprise upon seeing her standing nearby, either because she was very quiet when she approached or because she was there the whole time and they only just noticed her.
Sometimes she finds it funny, seeing people's reactions to her. She often thinks back to when the Kagamine twins first met her.
"Why don't you talk much?" Rin had asked rather rudely, earning a nudge from her brother. "What? I'm just sayin'!"
Len gave her a disapproving look. "She doesn't have to talk if she doesn't want to. Besides, you're not exactly the best at polite conversation."
This made Rin somewhat indignant, and the resulting argument was enough to draw attention away from Luka. Not that she minded. She never liked being in the spotlight for too long anyway.
Even so, she still overheard some of the things Rin would say about her whenever she was around. She always tried to whisper them, but she didn't really have the best indoor voice, so Luka would manage to catch some of her words.
"Creepy...weird...half-expecting her to murder someone…"
But then Len would scold her or give her a light slap on the shoulder for being so inconsiderate, and she'd give a half-hearted apology, but not before shooting the pink-haired woman another wary look.
At first, the comments had hurt, but Luka got used to them over time. In fact, when it had gotten to the point where they no longer affected her, she found the young girl's behavior rather amusing. Eventually, Luka even started deliberately sneaking into rooms on purpose, if only to see Rin's startled jump upon discovering her.
Rin wasn't her only victim. Meiko and Kaito were also particular favorites of hers. While they weren't mean to her, it was sort of the house tradition to mess with Kaito, and Meiko always carried herself as the fearless type. Because of this, Luka got a kick out of seeing the looks on their faces when they turned around, only to find that she had been there for who knew how long. Sometimes she would even target Len, if only because he gave the girliest shrieks.
She never went after Miku, though. While scaring the others was all in good fun, she just felt bad doing it to her. Granted, on the rare occasions that Luka would scare her by accident, the teal-haired girl's reaction was by far the most calm compared to the others. She would gasp softly, but her face would quickly melt into a smile, and she'd chirp, "Oh, Luka, it's just you!" Then, she'd continue to chatter as if her presence didn't disturb her at all.
For whatever reason, even though she hated scaring her, Luka would always find herself replaying Miku's response in her head more than any of the others'.