Lust Geass manga volume 2 features story and art by Osamu Takahashi.

Souta and Rikka are officially boyfriend-girlfriend, but they still haven't broken the demon Zepar's curse. Then, one day, Makoto, who had seen Rikka's "grimoire," falls prey to the curse herself. She consults with Souta and they begin to have a side relationship to keep Makoto's symptoms under control. But then Makoto leans into her curse and doesn't even want to be free of it?! When the grimoire's curse catches Makoto in its clutches, Souta, Rikka and Makoto form a love triangle?!