Koga Saburo

The ancestor of Mochizuki Chiyome and a Japanese figure who Shuten-douji greatly dislikes. He is associated with the god TakeminakataWP of Suwa Grand ShrineWP.[3]

Detailed in the Suwa EngiWP, Yamata-no-Orochi placed a curse on Koga Saburo after Saburo committed the crime of trespassing on Mount IbukiWP and destroying a serpent's nest, passed down in the Koga Mochizuki bloodline.[4][5] He was cursed by the god of Mount Ibuki, Yamata-no-Orochi, and traveled through the underworld beneath the mountain, eventually returning to the surface as a demon.[6] Ibuki-douji was the one who rescued him and returned him to the human realm, and he refers to her as his elder sister because they are both connected to Yamata-no-Orochi.

Voice:
https://www.youtube.com/watch?v=Gt0cCvrlIjQ&list=PL-Hm3rGMVE2vq4WojFwEAvJppTa_-U2pJ&index=4 (At 4:18 he starts talking)

Personality:
Assassin likes his Master Dorothea. He sees his younger self in her. He often complements Dorothea's ability, though Dorothea admits that he sometimes overestimates her.[1]He claims to have trouble understanding Western customs, often addressing Dorothea as princess despite being instructed to call her a lady. He is curt, arrogant and condescending in battle, gleefully laughing while attacking and appears to take pride in the power he is granted.

Attributed to his divine nature, Assassin has a fickle side to him, which led to him choosing to be controlled by Tsuchimikado Yasuhiro's spell so as to impose a trial on his Master.

Assassin shows a great deal of respect and fear to Ibuki Douji, who saved his life, taking her apparently playful comments as serious threats.