I Became My Best Friend's Stepmom

My best friend sent me a wedding invitation, coincidentally for the same day as mine.

Upon closer inspection, I realized we were marrying into the same family.

However... I was marrying the older one, and she was marrying the younger one.

"Your taste is awful, how could you go for an old geezer?"

"Your taste isn't any better. At least the old man is healthy. The sickly one you're marrying might kick the bucket any day now."

After marrying in, we discovered that this family's harmonious facade masked a cesspool of filth.

It wasn't until we found hundreds of women's corpses in the basement that we realized this was all just a plot against us.