Yasu is Kinzo and Kuwadorian Beatrice's child and was born due to the result of incest. Yasu is at the same time Kinzo's child and grandchild. It is implied that she was DMAB, but reassigned and raised as female upon the cliff incident.
Yasu is the same person as Lion Ushiromiya, but only in the worlds where Natsushi rejected the infant given by Kinzo. Yasu plays the role of Shannon, Kanon, and Beatrice and is the true antagonist of the entire Umineko series. She is the true form of Beatrice and the true writer of the message bottles. Due to her belief that she is furniture, amongst other things, Sayo plans out the Rokkenjima Massacre.
Yasu loves Battler, George and Jessica—that's Kanon's love, Shannon's love and real Yasu's love (Beatrice's feelings for Battler). It's expected that Battler's sin is forgetting Yasu and breaking a promise after six years. Yasu was the child that fell off the cliff along with another servant 19 years ago, but had survived the incident. The child received an injury which made Yasu's body unable to make love (after Yasu learned the truth it became the source of the furniture complex and the duel between Shannon and Kanon). Genji and Dr. Nanjo saved the child, but kept this a secret from others to prevent another incestuous advance by Kinzo. At the age of nine, (age was lowered to ensure that the child wouldn't be found out easily) Yasu came back to Rokkenjima as a servant. Genji personally arranged Yasu's hiring, hoping to reveal the truth if a good opportunity presented itself.
