Days with My Stepsister Novel Volume 1 was written by Ghost Mikawa with illustrations by Hiten.

After his father remarries, Yuuta suddenly finds himself with a new stepsister: Saki, the greatest beauty at school. Neither of them is sure how to act around the other at first, but the two gradually grow more comfortable living together. Slowly, cautiously, patiently, two strangers become more. So begins an unlikely love story.

Days with My Stepsister Novel Volume 2 was written by Ghost Mikawa with illustrations by Hiten.

Yuuta Asamura is still figuring out how to interact with his new stepsister, Saki Ayase. But after finding they have more in common than expected, the two reach a comfortable equilibrium. Things start to get out of whack, however, when Saki fails one of her exams and asks for Yuuta's help. Then Yuuta's attractive college-age coworker, Shiori, invites him out on a date, and Saki finds a strange new emotion welling up in her heart… Just what is this feeling?

Days with My Stepsister Novel Volume 3 was written by Ghost Mikawa with illustrations by Hiten.

It's Yuuta and Saki's first summer vacation as stepsiblings, and they'll be working at the same bookstore! As Saki's coworker, Yuuta begins to see a side of her he hadn't noticed before. But after observing her new coworker for a while, Shiori makes a dark observation—if Saki doesn't ease up and stop pushing herself so hard, sooner or later she's going to fall apart. In order to help her, Yuuta will have to make a decision. Should he interfere in his stepsister's life, even if it means breaking their promise?