Doctor Souichi Tomoe, also called Professor Tomoe, was a villain in Sailor Moon S and the leader of the Bureau of Bad Behavior (also known as Witches 5). Most of the time his face is shadowed whenever he has his labcoat on. He creates Daimon pods to make into Daimon Heart Snatchers.
Tomoe was a good scientist until he and his daughter were caught in a lab explosion caused by the demon Germatoid, who worked for Pharaoh 90, and possessed him in exchange for saving his daughter Hotaru from the explosion. Tomoe became evil from here, and searched for the Purity Chalice so he could awaken Pharaoh 90. To do this, he would need to find three treasures located inside the Pure Hearts of three people. He sent his assistant Kaorinite to find them, but she never did, and was killed by Sailor Uranus.
From here, Doctor Tomoe began creating more powerful Daimons inside a Heart Snatcher oven, and sent Eugeal of the Witches 5 to search for the three Pure Hearts. Soon she found them inside Sailor Neptune and Sailor Uranus, with Sailor Pluto's crystal ball being the third, and the Purity Chalice appeared. However, Sailor Moon got this, and Eugeal was killed by Mimet, the second of the Witches 5, who then took over for her to extract Pure Hearts to feed to Mistress 9, who was possessing Hotaru, whom Tomoe had chosen to be Mistress 9's host.
Soon, Mimet and the other witches were killed, but Kaorinite captured Rini and Mistress 9 took her Pure Heart to awaken in her true form. She send Tomoe over to fight Sailor Uranus and Sailor Neptune, where Germatoid left him and was later killed by Sailor Uranus. From here, Tomoe was no longer evil. He survived the battle with Pharaoh 90, though he suffered temporary anmesia and injuries to his arm and leg, resulting in him being in a wheelchair, but was expected to make a full recovery.
In the Sailor Stars arc, Tomoe is seen briefly enjoying life in the countryside with baby Hotaru, until Sailor Pluto shows up to take over on Hotaru's care. He was never seen again after.