Shuu is Kuranosuke's half-brother and a personal assistant to their father. Due to catching his father cheating with Kuranosuke's mother at a young age, he has a phobia of women. However, after first seeing Tsukimi all dressed up, he starts becoming attracted to her, though he cannot recognize her whenever she wears her normal clothes.

He later recognizes Tsukimi in her usual clothes and remains in love with her, accepting her immediately and encouraging her in everything she does. He also starts to visit her and bringing cakes. When Tsukimi feels down and cries he stays by her side. In chapter 49 he confesses his feelings to her but she misinterprets and then he decides to write her a letter to propose her marriage.