My Stepmother Took My Ex-Girlfriend and Asked Me to Call Her Sister

My ex-girlfriend turned out to be my sister! To be precise, my stepsister! In order to reassure their parents, the two of them each hid this secret. On the surface, they appeared to be very close and harmonious in front of their parents, but privately they were trying their best to quarrel with each other. After all, their breakup was due to unhappiness. But I never expected it! That night... They actually... This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.