Doctor Souichi Tomoe, also called Professor Tomoe, is a mad scientist, and the main villain of Sailor Moon S. He is the leader of the Bureau of Bad Behavior, but is working for Mistress 9 and Pharaoh 90. He is the father of Hotaru Tomoe, the husband of the late Keiko Tomoe, the maternal grandfather of Jesse and James Tomoe and also the father-in-law of Hiro Hamada.
Doctor Tomoe was not evil at all, but when a lab explosion caused by the Daimon, Germatoid, nearly killed him, and his daughter Hotaru, except for his wife Keiko who died during the freak lab accident; he let Germatoid possess him through his right eye in order to save his life.
From here, he became evil, and often his face was shadowed. He began creating Daimon pods, which he would use to create Daimons. His assistant Kaorinite and the Witches 5 were all working for him. It is unknown what exactly they are (like many main villains, they have a human appearance) or where they came from. He also chose Hotaru to be the host of Mistress 9, the Sovereign of Silence. Hotaru was unaware of Germatoid's presence within her father.
In Sailor Moon S, he sent Kaorinite to extract Pure Hearts, in search of the three Pure Heart Crystals that would make the Purity Chalice appear so he could awaken Pharaoh 90. When Kaorinite was killed, Tomoe invented a Heart Snatcher oven to put Daimon pods and items in to make Daimons that Eugeal, and later Mimet, would take with them.
Shortly before Eugeal's death, the Purity Chalice was awakened, but Sailor Moon got it. Afterward, Tomoe was ordered to get Pure Hearts to feed to Mistress 9, so he sent Mimet to get them.
At one point, he was playing Twister with the Witches 5 (Telulu, Byruit, and Cyprin were shadowed). At another, it is revealed that he brought Kaorinite back to life. At another, when he was out of his lab, Mimet crammed his Heart Snatcher Oven full of board games, causing the house to shift into another dimension, locking Tomoe outside, and forcing him to rely on the Sailor Scouts to save Hotaru, who was inside at the time.
Once Mistress 9 was awakened (though Kaorinite and the rest of the witches were killed in the process), she used the remaining Daimon pods to create a barrier of nameless Daimons. When Sailor Uranus and Sailor Neptune entered Mugen School, Mistress 9 sent Tomoe after them. He encountered them in a room full of several lifeless monsters of his creation. Afterward, Germatoid left Tomoe, no longer needing him. After an attack by Sailor Uranus, he took control of the monsters, but was killed by Sailor Uranus.
From here, Tomoe was no longer possessed, and arrived at the battle with Pharaoh 90, trying to protect Hotaru from him. He survived the battle, though with an injured arm and leg, putting him in a wheelchair, and amnesia, but was expected to make a full recovery. Amara and Michelle returned Hotaru (who was turned into a baby from the battle) to him. In Big Hero 6: Hiro's Return, he was completely loses his villainous nature after he accepts Hiro Hamada as his son-in-law.
Doctor Tomoe does not appear to have any attacks.
- He has a slightly similar appearance to Prince Diamond, and both are being manipulated by a bigger villain. The difference is, Doctor Tomoe was directly possessed by Germatoid, while Diamond was simply being manipulated by Wiseman into wanting revenge.
- At one point, in Episode 27, Thorny Weather, when Rini is ringing the doorbell, and Doctor Tomoe is looking around (his face shadowed), it looks like he is sticking up his middle finger (and he is standing in front of Mistress 9 at the time).
- His real name (Souichi) is shared by a young boy from Yu Yu Hakusho ,Kurama a demon that escaped to the living world raised as a human named Souichi.
- Hotaru Tomoe (daughter)
- Keiko Tomoe (wife, deceased)
- Hiro Hamada (son-in-law)
- Jesse Tomoe (granddaughter)
- James Tomoe (grandson)
Voiced by Jeff Lumby