My Sister's Best Friend, My Lover.

Vol.2 Chapter 10.5: Volume 2 Bonus & Extras
Vol.2 Chapter 10
Vol.3 Chapter 11
Vol.2 Chapter 10
Vol.3 Chapter 11
Sena is a novelist who has been dealing with romantic feelings for her sister, Yuuna. Upon learning that Yuuna is to be married, Yuuna's best friend and former lover Kiku asks Sena to be her lover...