Pheles Knowledge loved the library.
Pheles loved the many books that the Scarlet Devil Mansion had. There were tomes filled with ancient rituals, codices cataloguing the many species that dwelt in Gensokyo, and history books that offered many explanations as to how Gensokyo came to be. It was also the place where her parents spent most of their time when they weren't out visiting friends or spending a bit of time with Remilia and the rest of the household.
However, Pheles noticed a bit of a trend. She was used to the black-and-white witch crashing into the library in order to look at the books. However, she also noticed how distressed her mother tended to get whenever Kirisame Marisa visited the library alone. It didn't happen often; Marisa was often accompanied by Alice during such visits. Still, there were occasional lone visits and Pheles could swear that her mother was often a hair trigger away from grabbing a chair and throwing it at the witch to drive her off.
Pheles had just finished up reading a book on demon summoning when she heard the doors to the library being thrown open. "Patchouli! Are you in?" the unmistakable cheerful voice of Marisa called out. "Hm? Oh, hey there, Pheles! What are you reading?"
"Hi, Ms, Kirisame," Pheles replied, smiling shyly. "It's a book about summoning."
"Summoning, huh?" Marisa smiled. "Sounds cool. Are you going to summon a totally badass familiar someday?" Pheles nodded vigorously, causing Marisa's grin to widen. "Good luck with that, kid," Marisa laughed as she ruffled Pheles's light purple hair. "Say, where's your mother, anyways? I need to ask her for some books."
"She's sleeping right now." The voice belonged to Pheles's father, a devil simply known as Koakuma. "What books do you need?"
Just as Marisa left the Scarlet Devil, Patchouli came running armed with a letter opener. "I heard Marisa in here a moment ago," she gasped out. "Was she alone? Did she do anything to the library? Did she steal anything?"
"Calm down, Patchouli!" Koakuma cried as she ran over to steady her still somewhat unsteady wife. "She just borrowed three books and I made sure to note which ones she took. Don't worry about it, alright?"
"But...but what if she..."
"She would get a tongue-lashing from her wife, that's what," Koakuma assured her. "Now just sit down, put the letter opener away..."
"Daddy, why does Mommy not like Ms. Kirisame that much?" Pheles asked, unable to contain her curiosity any longer. Koakuma looked a little alarmed at her child's directness but Patchouli was more than willing to answer.
"It's not that I don't like her, it's that her past visits almost always ended in disaster! She would steal books and never return them and often caused danmaku battles to happen in the library! It's a miracle Sakuya didn't get tired of cleaning the place up after her rampages here!" She took a deep breath. "I...I know she's gotten better and doesn't do it anymore, but I still get a little nervous." She motioned for her daughter to come closer and pulled her into a hug. "So don't think Mommy hates her, alright? I just have a few bad memories."
"Alright, Mommy." Suddenly, Pheles frowned. "Is that why you woke up that one time screaming her name and yelling at her to give back your books?"
"...I need to count the books here." Patchouli made to get up before Koakuma grabbed her. "Let me go, Koa! She might've taken some without you noticing!"
"No she didn't! Pheles, help me get your mother back to bed!"