There is a literary name called "Meteor Collision"
A short story, slightly scary.
The attribute of this younger brother is probably that he is as docile as a dog (little milk dog) in front of his sister, but as ruthless as a wolf (little wolfdog) when her sister is not there, and he is also a little yandere. He switches seamlessly. This is why he is so famous for his double standards!
Come, let's take a tour of pseudo-orthopedics~
Intention: Reunion after a long absence