Sen (「千両」?; Sen ryō; 1,000 ryō) is one of the two actor demons that have taken over the Playhouse, his partner being Ryo. He is indirectly fought by Chibiterasu and Kagu when they face the giant mechanical doll, Renjishi.
As stated by an actor at the Playhouse, Sen, like his stage partner, Ryo, was once human, but his dreams of becoming a well-known actor were never realized. Once Sen had died, his resentful spirit became a demon much like King Fury, and all were later unknowingly infused with the evil essence of Yami.
Sen is a crane demon, similar in appearance to a Crow Tengu or Ubume. His wings are a mix of orange, yellow and brown and seem to be connected to the kimono he wears. He has a cloth around the back of his head resembling a traditional Japanese woman's hairstyle, complete with pins sticking in it.
Sen is first mentioned when Chibiterasu and Kagu arrive at the playhouse, though he is only named as a demon by the humans, and by the demons as their master. He only makes an appearance right before the battle against him and his partner Ryo, when the two try to take the stage in order to perform their play. Chibiterasu and Kagu then fight the duo and their mechanical doll Renjishi, defeating the two actors for good. Just before they die, they mourn the fact that they could not live up to King Fury's expectations, this being the first time his name is mentioned.
Also, there is a term "Sen ryō Yakusha" (「千両役者」?; せんりょうやくしゃ) referring to famous actors.
Sen is designed in the motif of a crane, a symbol commonly known throughout East Asia as a representation of 1,000 years longevity.
↑"Miss Kagu, do you know about Sen and Ryo? Those two evil spirits were once aspiring actors. They tried out for different parts, but they were terrible. They died without ever being able to set foot on a stage. Only after they became Yōkai spirits did they achieve their dream. It's quite ironic... and tragic..."—Actor (Ōkamiden)
↑"Hey there, doggy. You're lucky you're an animal, cause humans can be pretty greedy. They only look out for themselves and have petty jealousies. Sen and Ryo's greed caused them to be reborn as evil Yōkai. I don't see how humans can say they're better than animals like you."—Actor (Ōkamiden)