Thank You For Loving Me (Inspire by Yosuga no Sora)

Aya Kizuna just has turn 17 and Kenichi Kizuna is 18.
The 2 siblings have been living together for 4 years since the death of their parents. Kenichi has been taking care of Aya for 4 years. They also have a close relationship.
One night, after Kenichi came home from his girlfriend Mina’s house, something strange happen. Kenichi begins to show these emotions towards his sister that she has never thought he has for her.
PS: I was watching Yosuga no Sora