Getting along with a siscon was actually quite troublesome. The simplest example:
If you praised their little sister, they would very likely suspect you of harboring ulterior motives toward her. Could they tolerate that? Of course not, so they would fall out with you!
But if you chose not to praise her and instead pointed out her flaws, they still could not tolerate it. Could a little sister's flaws even be called flaws? Time to fall out!
You could neither praise nor criticize her, so you might as well ignore her—but in reality, that would not work either. If you could even ignore their beloved little sister, what right did you have to be their friend? Fall out, fall out!
Take Yukinoshita Haruno right now. Though she knew that anyone in the know could tell at a glance that her little sister had an air of wealth about her, once it was pointed out right in front of her, even if she could not fall out with him, she would still say:
"Bastard, what do you know about looking slim in clothes but having curves underneath? Little Yukino just doesn't look like it, but she's actually super well-endowed..." Even if she had to lie, a HENTAI siscon had to protect her little sister's dignity.
"Lady Haruno, summer is almost here..." Sogo Doma glanced at her.
"So what?" Yukinoshita Haruno asked in confusion.
"Once summer comes, swimming classes should start too. Whether someone is well-endowed should be obvious at a glance, right?"
"..." Yukinoshita Haruno fell silent.
"Looks like you agree." Sogo Doma chuckled.
"Little Yukino's second growth spurt is just a little late..." Yukinoshita Haruno offered her theoretical basis.
"She's sixteen..." Sogo Doma spoke with facts.
"The Yukinoshita Family's genes don't produce flat chests..." Yukinoshita Haruno submitted genetic evidence.
"So