邪淫のいけにえ外伝 シスコン兄貴、妹が好きすぎて触手になってしまう

Hirosaka Kouta lives together with her younger sister, Kaede, due to their parents' jobs. He is an honor student with excellent grades at school. However, he is a severe siscon and loves Kaede from the bottom of his heart.

One day, He accidentally drops his phone in a plant when coming home from school.
When he tries to pick it up, he gets bited by an unknown being, presumably an insect.
However, the wound soon disappears as if nothing had happened.