"Jacob, I forgot to bring my underwear. Can you pass it to me?" Mia's voice, mixed with the sound of showering water, called out.

Even though I was also in the living room, she asked my husband, Jacob, to fetch her underwear for her.

After all, there should be boundaries between men and women, even if they are siblings, so I said to my husband, "Where's Mia's underwear? I'll get it for her."

Jacob, accustomed to this, replied, "It's okay. She's always been careless. I'll bring it to her. You don't know where it is."

Insisting, I made Jacob hand the underwear to me.

When I entered the bathroom, Mia stood there naked, her youthful body fully exposed before me.

"Jacob, can you help me put it on..."

Seeing that it was me, Mia screamed, "Why is it you?"

I handed it to her, kindly asking, "Do you need help putting it on?"

Mia pushed me out and slammed the door shut.

I felt something was off.

Thinking Mia had just started university last year, still young and never having been in a relationship, she might depend on Jacob somewhat.

Although my husband and I lived in the same city as Mia, she rented a place near her university, and Jacob often traveled for work, so they hadn't spent much time together over the year.

This holiday season, Jacob and I returned to his mother's home, and Mia was on winter break, so the siblings had a chance to spend time together.

Once dressed, Mia looked at Jacob sitting on the couch and cooed sweetly, "Jacob, I'm on my period recently. Can you wash my panties and bra for me?"

I couldn't help but interject, "Isn't that inappropriate?"

Jacob immediately sat up in defense. "What's the big deal? I used to bathe Mia when we were kids! It's just underwear. Don't overthink it!"

Saying so, he rushed to the balcony and vigorously scrubbed Mia's underwear.

Jacob and I usually washed our own intimate clothing separately, and I had never seen him so eager to help me wash anything.

During dinner, Mia placed her legs over Jacob's, and the two of them sat very close together, seemingly seeing nothing wrong with this, as if it were routine.

Mia passed a large plate of shrimp to him. "Jacob, peel these for me!"

She then watched videos on her phone, laughing loudly and hugging Jacob's neck whenever something amused her.

This seemed outrageous to me. Even the closest siblings wouldn't behave like this, right?

My mother-in-law seemed to notice my discomfort. She chuckled and explained, "They've always been this close since they were little. You're an only child, so you might not understand."

"If you had twins for the family, you'd know!"

I just thought I was overthinking it.

But the outrageous was yet to come.