Rosen Garten Saga, Volume 1 (Rosen Garten Saga #1-5)

Lyn's village falls under attack by bandits and amidst the chaos she gets her hands on a special sword. The sword turns out to be a magic sword that houses the soul of the great hero Siegfried, and with its power Lyn makes short work of the bandits. However another throbbing "sword" has sprouted from between her legs?!