The male protagonist of 'My In-Laws are Obsessed with Me.' A handsome man with black hair, red eyes, and a pompadour style. He is the youngest of three siblings and inherited the position of family head after his older brother's death. Hair color: Black The current Grand Duke and head 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 when she comes to propose a contract marriage. When Pereshati collapses, he assumes she is dead and tries to bury her, but upon seeing her wake up perfectly fine, he feeds her his blood once more as an experiment. After realizing that the Lapileon curse does not affect Pereshati, he enters into a contract marriage with her. As time passes, he comes to truly love Pereshati.

The adopted son of the two protagonists and the heir to the Grand Duchy. Hair color: Black Therdeo adopted Celphius to ensure the succession of the Lapileon family. Therdeo sent Celphius to a separate villa out of a desire for the child to grow up freely in a good environment without pain. However, because Therdeo rarely visited or spoke to him even at the villa, the servants there often gossiped about Celphius. Consequently, Celphius developed a habit of enduring everything to be recognized, believing the Grand Duke only adopted him because he needed an heir. He gradually comes to follow Pereshati sincerely, viewing her as a mother. Later, Pereshati gave Celphius permission to call her 'Mom.' Also, since he is the same age as Islet, who was rescued from abuse, he takes good care of her and they get along like real siblings. He was the first person in the Lapileon family to open his heart to Pereshati.

The Grand Prince of the Lapileon family, the family physician, and the uncle of Sercia and Therdeo. Hair color: Black He is a talented individual who researches the Lapileon curse and prescribes medicine. Several members of the Lapileon branch families work under him. In his youth, he ran away from 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 couldn't bring himself to leave the lone Therdeo behind and stayed. He has effectively played the role of a father to Therdeo. However, regardless of his decision to stay, his feelings toward his mother seem to remain poor. When he suggested that Therdeo let Pereshati go, Therdeo addressed him coldly as 'you,' saying that someone who had once abandoned the family had no right to speak to him like that, suggesting unresolved tension between them.

The first Grand Duchess and the grandmother of the current Grand Duke Lapileon. Hair color: Silver There is no one in the Empire who doesn't know her. First, because she married someone from the same family (though distantly related), and second, because she was the only one to engage in social activities from the reclusive Lapileon family. Currently, she resides in the Grand Duchy after passing the title to Therdeo. It seems she did not 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 even ordered her husband's portrait to be turned face-down. She pities and tries to be as considerate as possible to branch family members like herself, but she is said to be equally strict.

The former heir of Lapileon and Therdeo's older sister. Hair color: Red After her older brother died and a new head had to be established, she wished to create a family without the curse, starting with her own children. Just as 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 both her husband and son to die. Due to this, she gave up the succession and fell into madness. She is gradually recovering while managing the Lapileon family's businesses. She is the second person in the Lapileon family to open her heart to Pereshati.

An ill-fated princess who was born naturally weak and was slowly dying, unable to leave her sickbed. It is said she recently recovered from her illness. Because the Emperor pushed for a marriage between Dodorea and Therdeo, Therdeo hurriedly held a wedding with Pereshati. She shows an unusual obsession with the Grand Duke, whom she barely knows, and acts hostile toward Pereshati. She often appears to have no sense of morality and makes delusional claims, such as saying that many people, including herself, suffered because of Pereshati's intervention. Dodorea's true identity is the witch who cursed the Lapileon family. The real Dodorea died after her body was taken by the witch, but she watched the Lapileon family—who were essentially headed for extinction due to the curse—even in death. To save them, she caused Pereshati to regress and appeared in Pereshati's dreams to reveal the whole truth.