I managed to find the full PV of Waremete’s OP. The single is slated for release on 22.10.2014, which is actually in a few days time. I personally find the OP to be one of the better ones for Autumn alongside with Sora no Method’s.
The song is sung by Satou Satomi, a voice actress notable for her roles as Wendy in Fairy Tail, as well as Eru in Hyouka a few years back. She plays a minor character of Karin Fukazawa in Waremete, too, as with the tradition of most eroge adaptations, where the singer of the theme song would only feature as cameos.