Asuka Higuchi falls for her half-brother Manato Sudou early on in the story, and he eventually comes to reciprocate.
Knowing one is definitely his sister doesn't stop him from wanting them BOTH.
No, they're full-blown siblings.
This is what makes it especially damaging.
Instead she just succeeds in getting MC's best friend to kiss MC much to his sister's despair and anger.
Then again, this is a show that's filled to the brim with fetishes.