As childhood friends, Rias and Sona have a great deal of respect for each other, as well as a friendly rivalry. Sona cares for Rias a great deal and wishes the best for Rias. After Rias told Sona about Issei confessing to her, now Sona wishes to have a boyfriend.
Sona became observant of Issei upon hearing that his revival cost eight Pawn pieces. During Rias' first Rating Game against Riser, she was quick to be disturbed by Issei's Dress Break. Later on the series, Sona has grown to admire and respect Issei very much and is also jealous at the same time because Issei relieved Rias of many of her problems that she had but she could not do anything for her because of her position as a High-Class Devil and her family's rank in the upper society of Devils. She cares a great deal for Rias as her friend and wishes for Issei to give her a strong support because she is stubborn and willful but at the same time delicate. In Volume 11, she suggests Issei to call her by her first name whenever they are alone, but Issei couldn't and she gave a small laugh. Sona congratulated Issei on the recommendation for his promotion to Middle-Class Devil and wishes him to give Rias as strong support as possible. She also congratulated him on his growth after he defeated Sairaorg Bael.
Akeno and Sona are good friends outside of social standing, calling each other by their first name when in private.
Sona is strict with Saji and always scolds him when he is making a fool of himself. Saji is in love with her, and while she seems to genuinely care about him, she states that she sees him more as a younger brother and wouldn't lay a hand on him since two other members of her peerage are in love with him.
He respects Sona's feelings to the point he will endure eating her disgusting cakes to make her joyful and not disregard the feelings she puts into making her cakes as thank you gifts.
Sona first met Tsubaki shortly after she arrived in Japan and quickly made Tsubaki into her servant. The two have since had a good relationship with each other. Sona even stated that she was glad to have met Tsubaki, a sign of their closeness.
Sona is often embarrassed by her sister's child-like personality and her overprotective nature. Despite so, she does genuinely care for her sister. Sona herself is also quite protective of her sister stating she wants to keep "bugs" away from her. The two sisters have very weird tastes as Serafall really likes the 'destructive level' cakes as described by Issei that Sona makes and will come down on anyone who openly states they dislike them, as it will break Sona's heart.