Heavenly Chief Star, Mephistopheles Yōma is a Specter. He appears before Gemini Aspros to thwart his attempt on Hades’ life, as he seeks revenge for his reincarnation of Earth. It is later revealed that Yoma is Kairos, a former Time god and the younger brother of Khronos, a superior god of time.
As Kairos, Yoma was originally a god of time, specifically of opportunities and special moments. However, he has stated to have been defeated and sealed into a human form by the gods, including his brother Khronos. Unlike other gods, Kairos’s incarnation was forced, making it so that like other humans he can age, be harmed and also die. On Earth, Youma was born in Japan, but traveled abroad, feeling sufocated with the shogunate’s peace, as his evil star woke up inside him. One day, he saw a comet pass through the sky; it was the Pegasus spirit. He followed it through the sea, until he reached a foreign land (Germany), where the Specters who had their evil star awakened reunited. He soon encountered the Heinstein Castle, and met Partita, in whom he found the Pegasus spirit.
While tracking the spirit of Pegasus, Yoma passed by the Sanctuary in Greece, where he found the young Aspros training alone. He asked him where the Pegasus saint was, to which Aspros replied that there was still no Pegasus Saint yet. He then asked if he wouldn’t train with another young aspiring Saint he saw. The young Saint said that was Defteros, his younger brother. Yoma says that he likes the seconds, as they aways want to kill the firsts. Aspros angrily says his brother would never do that, just to see that his brother is training around, with a power alike to his own. Surprised, he doesn’t realize Yoma was planting a seed of darkness in him, which would later ruin his life.
After arriving at the Heinstein Castle, Youma became one of the servants of Pandora’s family, and marries Partita. She soon becomes pregnant, giving birth to their son Tenma. Some time after that, Youma steals the newborn Hades, Pandora’s brother, and take him away from the castle, and thereby from the twin gods Hypnos and Thanatos. He hides Hades within the purest child in the world, Alone, and, disguising himself as a priest, Yoma gives the newborn to a lovely couple. He soon watched Athena, the goddess of wisdom and Hades’s archenemy, reincarnate as Sasha, the sister of Alone, and his own son Tenma going to live in the same foster care with the two gods after Partita’s untimely death; Yoma becomes excited about how this would proceed.