Professor Tomoe wasn't always evil. He was once a normal human being; a physicist / scientist whose wife died in a house fire long ago. He has a daughter -- Hotaru, whom he cares a lot about, enough to give up his own soul for her life.

Some time ago, when Hotaru was very little, about 6-9 years old, Professor Tomoe was explaining his new invention to the other scientists. Hotaru noticed something glowing through the glass case and inquired about it, Professor Tomoe told her not to get too close as it was dangerous when all of a sudden, his invention blew up! The explosion killed everybody in the lab except him. He was holding Hotaru in his arms. He was crying when the Daimon Master appeared, and asked Professor Tomoe if he really wanted Hotaru back. Professor Tomoe said "Of course I do! Anything!". The Daimon Master then made a deal with the professor. In exchange for Hotaru's life, the Daimon Master will possess Prof. Tomoe's body. Professor Tomoe agreed and so Hotaru was brought back to life and the Daimon Master possessed the professor's body via a glass lens that went into one of Prof. Tomoe's eyes. The now evil Professor Tomoe allows the entity Mistress 9 to possess Hotaru's body as well. Professor Tomoe is a genius and he creates the Daimon eggs, thousands of them and sends them out to find the pure heart crystals: first for the talismans, then for the right one to revive Mistress 9. The Deathbusters' objective is to summon Master Pharoah Ninety by using the Holy Grail. He in turn will wreak havoc and death upon this world.

Professor Tomoe wears a lab coat most of the time and at first you never get to see his face, you only get to see 2 white circles which are his glasses that glow. He has this insane laughter and when he is in public, his face is visible and his glasses stop glowing. Even when evil, he loves Hotaru.

In Sailormoon S, the Daimon Master leaves his body and he recovers in the hospital to take care of the reborn baby Hotaru. In the manga, he dies.