Shitei Furin ~Hitozuma Sado Ane to no Kinshin Kozukuri~

The protagonist has been secretly in love with his sister for many years and was last year she got married. His sister and her husband came to visit for 5 days but on first day husband had to leave. The protagonist plotted to try and steal her away from husband as this was his best chance. But would be in for a surprise when things take a turn he wasn't expecting.