Doguchan: The Ancient Dogoo Girl (2009)

By chance, a hikikomori named Makoto Sugihara finds a strange breastplate buried in the woods. When he places his palm on the breast plate, its design gets burned into his palm while the action awakens a girl named Dogu-chan, a hyperactive youkai hunter from the Joumon period with large breasts. Because he had touched her breastplate, Makoto is now bound to Dogu-chan as she adapts to modern day life, fighting youkai in magic armor formed by her doguu assistant Dokigoro while slowly prying Makoto out of his shell as he is dragged into her misadventures, whether he likes it or not.