Shisei Houjou
About
Shisei is a kind girl who loves her cousin Saito, she will console him whenever Akane gives him a hard time, she has told Saito that if he ever became homeless she would join him on the streets.
Shisei does have a mischievous side as seen when she found out about Saito and Akane's marriage and demanded Hush money from Saito, but this was probably a joke.
She is Saito Houjou's cousin. With a doll-like appearance and a captivating, cool demeanor, she shares a close friendship with Saitou, having grown up with him as if they were siblings. While she acts very simple and affectionate, she also is insightful when Saitou relies on her.
As a part of Houjou bloodline, Shisei was born with high IQ inherited from her ancestors.
(Source: I'm Getting Married to a Girl I Hate in My Class Wiki)