I decided to become a familiar. by Thunder Beast

Nagi, a high-ranking monster who suffered a serious injury, is rescued by a human named Kanata and survives. When Nagi learns that Kanata will undergo a summoning ritual in a year and a half to obtain a familiar, Nagi decides to reveal herself as a high-ranking monster—a Thunder Beast—during the ceremony and become Kanata's familiar. Three episodes total. The main story is complete. From the Thunder Beast's perspective.