Tsuchiya Sera

About
Sera is the sheltered ssister of Tsuchiya Kuon. She is quite sickly and is one of the main driving forces of Kuon to be successful. Yagami Keiko takes care of her as well as Kuon.

Kuon took it upon himself to care for her after their parents died. Taking care of her was the main reason for Kuon to actually put up with Tsuchiya Wakako. She took her last name as her brother did so as well.

Her life mostly consisted out of staying inside to prevent getting sick. Kuon spoiled her quite a lot to make sure she doesn't get too bored. As a result of her demeanor is rather innocent, unknowing and childlike. The one thing she truly cares for is her brother.

Her love for her brother seems to make her capable of doing pretty horrible things. She seemed to routinely punish Tsuchiya Yuki for taking her brother away and for her seemingly being loathed by him. She did so by cutting her up with roses and needles. At some point she feels that Kuon hates her so much that she should just die, which she doesn't mind at all. She does not seem to understand that what she did was bad and she finds Kuon's reaction to be close to bullying her. Her ending has her have sex with her brother and her brother then forcing her to commit suicide with him due to his regrets in raising her. If she is stopped, she just gets really upset at Kuon as she does not understand why.

She also becomes great friends with Kagami Sayo. Her, Sayo and Kuon become like family together. She sometimes feels a bit jealous of Sayo's closeness to Kuon and says as much. In her version of that route they move to Switzerland and live a slow, comfortable life.