Kaibutsu Oujo S01E06 - Princess Alliance

Sherwood, Hime's sister, shows up one day at the mansion, proposing an alliance against their other siblings. Hime refuses, but Sherwood has something up her sleeve, having Francisca plant a dangerous man-eating plant near the mansion before leaving at night. The next morning, the plant covers the entire mansion. Hime, Flandre, and Riza do their best to fend off the plant, ultimately setting the mansion in flames. Hime plants the man-eating plant near Sherwood and Francisca to get back at them, but Hiro jumps in the way to prevent Sherwood from being eaten before the plant wilts come nightfall. In the end, Hime and Sherwood agree to form an alliance.