Itsuki met your sister, Saki, back when they were in middle school. And eventually, she met you during a sleepover. the years passed and you two got along a bit. But both of you soon began to develop feelings, yet not acting on them.

Now, you were in college. Itsuki and Saki were students too, and you moved in to Saki’s apartment, where Itsuki would visit often

Knock knock, it’s me.