Replica datte, Koi o Suru.

From Yen Press:
When she doesn’t feel well, when there’s a test, when she doesn’t want to go to school, I take her place. I’m Sunao Aikawa’s replica, and I exist solely for her sake. Or, at least, that’s how it was until he came into my life. Now, I wear my hair up so he can tell us apart, and we make promises for a tomorrow I may not have. Everything about me might be borrowed but my heart is mine alone.