Days with My Stepsister, Vol. 2 (novel)

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?