|First Appearance||Tenchu: Stealth Assassins|
He is the Demon King and has Onikage as right hand man. He is also referred to as "the Lord of Hell." Mei-Oh's first real mention is when his forces kidnap Kiku. He dies by Rikimaru (or Ayame) in the end of Mission 10: Free the princess.In Tenchu: Wrath of Heaven he is mentioned by Rikimaru in the mission: Find the Shichishito Sword. In Ayame's story, Tenrai offers himself to Mei-Oh' spirit after being defeated, and absorbs his power and two of the jewels he had collected, but Ayame still defeats and kills Tenrai.
In Rikimaru's story however, Tenrai demonstrates the power that Mei-Oh can offer, and uses it to attack Rikimaru, after an intervention from fellow azuma ninja Ayame he musters the strength to kill Tenrai.
After Rikimaru defeats Tenrai and the battle ends, the previously thought deceased Onikage appears and converses with the impatient spirit of Lord Mei-Oh stating that his time to return has finally come. Lord Mei-Oh isn't mentioned in Tenchu: Shadow Assassins, but from Onikage's plans it must have arranged during Tenari's demise to bring all of Gohda and his domain to breaking-point. It is unknown if Lord Mei-Oh wants to recruit Rikimaru or it's just Onikage's intentions, but he is mostly like going to get Ayame, as she wasn't loyal to Gohda but Kiku and would possibly wanted kill Rikimaru.
Mei-Oh possesses immense magical power and with his sword Shichishito, he has powerful attack. He is able to teleport, although just for short distance.
- Mei-Ō (冥王) literally means "dark monarch". It is also the Japanese word for Pluto, the god of the underworld in classical mythology, while being more common in Japan the use of the word Purūtō (プルートー).
- He shares his name with Grandmaster Meio, an villain character from the Strider series, and they both share similarities.