Pretty standard bro-sis incest premise. The reason Cross Account didn't have more legs was because it was so bog standard in concept and execution, so the author really needs to do *something* to make his next series stand out compared to the rest. Aside from the art, what makes this stand out from the forbidden eroticism of siblings dating in secret like in Siscon Ani or the sexual tension between siblings aware their forbidden feelings are mutual like in Binetsu Kuukan?