The kidnapped human princess. Though she is technically a captive, she lives quite comfortably in the Demon Castle—so much so that the monsters are the ones who seem pitiful. She constantly plunders materials from the monsters to craft better bedding. Most monsters call her "Princess." She roams freely throughout the castle and gives the monsters nicknames: Demon King Tasogare is "Tasogare" or "Demon King," Leonard is "Leo," Red Siberian Kai is "Fluffy Dog," Poseidon is "Fish-kin," Hades is "Fish-kin's Big Brother," and Sand Dragon is "Sand Spa."

A monk at the Demon Castle's underground church. He is in charge of resurrection, specifically for the Princess who dies constantly. The monsters usually call him the "Demon Monk." He appears gentle, but he gets so jealous of any man approaching the Princess that he even makes voodoo dolls. He is always stressed because of her. He speaks politely.

The Demon King. He is the one who kidnapped the Princess, but he is currently the number one victim suffering because of her. He is distressed that the Princess's destructive behavior seems to be worsening. The monsters call him "Lord Demon King." Despite his title, he isn't scary at all. Even the residents of the castle don't really perceive him as a threat. He is 100% a novice at being evil.

The Demon King's pet dog. He has a humanoid frame but the body of a dog—essentially a dog that walks like a human. He strictly adheres to rules and regulations, much like a disciplinary committee member. He used to be much smaller than the Demon King, but he has grown into a large dog that surpasses the Demon King's height. He is a loyal dog who restrains the Princess when she goes on a rampage. He likes the Demon King (not romantically) and is obsessed with Demon King merchandise.

The God of the Sea. He is about the same height as the Princess, but his age is estimated to be in the 50s or 60s. However, his mental age seems similar to the Princess's. Since human faith has declined, he has been reincarnated in a demonic form. He is always bickering (physically) with the Princess. He has a very prickly personality. He wants to get along with his older brother, Hades.

To put it bluntly, a shut-in. She is always holed up in her laboratory and only comes out when she has a specific purpose. You cannot meet her unless you visit her directly. She used to be friends with Leonard, but now she seems to have forgotten how to interact with people. Unintentionally, she can come across as rude. She always covers her face with one hand and speaks while hiding behind things like walls.

Despite the name, he is currently in a male humanoid form. He can transform into a dragon, but he is currently in energy-saving mode after being defeated by the Hero. When he gets angry, sand pours from his body. The Princess used this to create a sand spa and calls him "Sand Spa." He originally had anger management issues, but he has been trying to control his temper since losing to the Hero. Lately, he keeps breaking his glasses and emitting sand because he can't hold back his anger toward the Princess. He uses polite speech to try and appear gentle.

The God of the Underworld and Poseidon's older brother. Like Poseidon, he was reincarnated as a demon due to a lack of faith. Syalis says his beauty is explosive, and he loves fur coats. He is actually prickly but has a warm side somewhere. He wants to be on good terms with Poseidon.