Days with My Stepsister, Vol. 5 (light novel) Ghost — Ghost Mikawa

Yuuta and Saki begin a secret double life and a relationship they can't name -- they're still siblings, but they're also teens in love. Going on their first date, getting into fashion, attending a friend's birthday party, celebrating Halloween. They've lived their lives without expecting anything from others, but as they spend more and more time together, those feelings begin to change. And gradually, the people around them start to notice...