The male protagonist of 'My In-Laws are Obsessed with Me'. A handsome man with black hair, red eyes, and slicked-back pomade hair. He is the youngest of three siblings and inherited the position of family head after his older brother's death. The current Grand Duke of the Lapileon family. He is at the forefront of wars and suppressing rebellions. The Lapileon family carries an ancient curse where their blood is poison. Therdeo also has toxic blood and accidentally feeds his blood to Pereshati, who came to propose a contract marriage. When Pereshati collapsed, he thought she would surely die and intended to bury her, but upon seeing her wake up unharmed, he fed her his blood again as a test. Afterward, he realizes that Pereshati is immune to the Lapileon curse and enters into a contract marriage with her.

The female protagonist of 'My In-Laws are Obsessed with Me'. A beauty with pink hair and gold eyes, described as being famous for her beauty in social circles. She was murdered with poison by her stepmother, stepsister, and husband, whom she trusted, and regressed to the time before she married her husband. To protect herself from her husband and family, she seeks out the Grand Duke Lapileon and proposes a contract marriage (which is initially rejected). Upon waking up, Pereshati hears the family secret from Therdeo: that the blood of the Lapileons contains a strong toxin. Pereshati is the only person immune to the Lapileon poison. She has caused various characters to warm up to her with her unique kindness, including Celphius, who felt abandoned by his uncle; Seresia, who suffers from the loss of her family; and Therdeo, who rarely shows emotion due to the closed-off family environment.

The adopted son of the two protagonists and the heir to the Grand Duchy. Therdeo adopted Celphius to ensure the succession of the Lapileon family. Therdeo sent Celphius to a separate villa out of affection, wanting the child to grow up freely in a good environment without getting sick. However, because Therdeo rarely visited or spoke to him even when he went to the villa, the servants there often gossiped about Celphius. As a result, Celphius came to believe the Grand Duke only adopted him because he needed an heir, and he developed a habit of enduring everything to be recognized. He gradually began to follow Pereshati sincerely, treating her like a mother. Later, Pereshati allowed Celphius to call her 'Mom'. Also, since he is the same age as Ailet, who was rescued from abuse, he takes good care of her and they get along like real siblings.

The Grand Prince of the Lapileon family, the family doctor, and the uncle of Seresia and Therdeo. He is a talented individual who researches the Lapileon curse and prescribes medicine. Several collateral members of the Lapileon family work under him. In his youth, he left home to avoid marriage under the pretext of researching the curse. When he returned and his eldest nephew passed away, he intended to leave the family again, but he stayed because he couldn't leave the lone Therdeo behind. He is the figure who practically served as a father to Therdeo. However, regardless of his decision to stay, his feelings toward his mother still seem poor. When he suggested to Therdeo that he let Pereshati go, Therdeo addressed him coldly as 'You' and said someone who had once left the family had no right to say such things, suggesting unresolved emotions between them.

The first Grand Duchess and the grandmother of the current Grand Duke Lapileon. There is no one in the Empire who doesn't know her, first because she married a man from the same family (though distantly related), and second because she was the only one to engage in social activities within the closed-off Lapileon family. She currently resides in the Grand Duchy after passing the title to Therdeo. It seems she didn't have a good relationship with her husband; Phineas recalls her arguing with him when he spoke of duties in preparation for her and the eldest son's death, and she ordered her husband's portrait to be turned around so it couldn't be seen. She feels pity for collateral members like herself and is as considerate as possible, but she is said to be equally strict.

The former heir of Lapileon and Therdeo's older sister. After her older brother died and it was time to establish the next head of the family, she had a wish to create a family without the curse, starting with her own children. Just when she felt this wish might come true with her husband's support, tragedy struck. Her son, saying it looked uncomfortable for her to wear gloves every day, took them off. While she was cooking for her husband and son in that state, a tiny wound on her hand caused their deaths. Because of this, she gave up the succession and fell into madness. Since then, she has been gradually improving while managing the Lapileon family's businesses.

The daughter of Zen, a collateral member of the Lapileon family. Due to the effects of abuse, she still has a fear of the red eyes unique to the Lapileons, so she covers her eyes. Since Pereshati has gold eyes, Ailet can look at her directly and follows her, calling her 'Sister'.