Rentarou Aijou is the central protagonist, a first-year high school student with messy brown hair, thick eyebrows, and a healthy, athletic build. After surviving one hundred painful romantic rejections during his childhood, he learns from a deity that he has been assigned one hundred soulmates due to a cosmic blunder. Driven by a deep sense of duty and genuine love, Rentarou acts as the ultimate selfless boyfriend. He regularly breaks reality, shatters manga panels, and pushes his physical body to absolute extremes to make sure that every single girlfriend feels completely cherished, protected, and uniquely valued.

Karane Inda is Rentarou's other co-first girlfriend. She has a slender build, sharp golden-blonde hair tied into long twin-tails, and highly expressive eyes. Karane is the textbook definition of a fierce tsundere, sporting a hot temper and a total inability to express her intense affection honestly. She routinely hides her deep vulnerability behind physical violence and loud denials. Despite her harsh exterior, she is fiercely loyal, deeply caring, and constantly acts as the essential straight man to steady the family's wilder antics.

Shizuka Yoshimoto is Rentarou's third girlfriend. She has a remarkably small, fragile stature, dark blue hair, and wide, quiet eyes. Shizuka is paralyzingly shy and suffers from severe social anxiety, making her an absolute bookworm who struggles to speak aloud. To cope, she communicates by pointing at specific lines of text within her favorite digital fantasy novel on her phone. She possesses a deeply gentle, innocent spirit and shares an incredibly tender, protective friendship with Nano Eiai.

Nano Eiai is Rentarou's fourth girlfriend. She boasts a tall, striking figure with long, straight silver-white hair and piercing blue eyes. Nano is highly intelligent and completely mechanistic, initially viewing human life, relationships, and emotions through a lens of strict mathematical optimization. She originally dismissed romance as an inefficient waste of time before Rentarou taught her to appreciate the beauty of feelings. She acts as the ultimate logical foil to the group and keeps a soft, caring spot for Shizuka.

Kusuri Yakuzen is Rentarou's fifth girlfriend. She possesses a bizarre biology that allows her to shift between a tiny, dark-teal-haired child form and a tall, beautiful eighteen-year-old adult body. Kusuri is a chaotic, hyperactive, and brilliant mad scientist who ends her sentences with the phrase "yep, yep." She spends her time brewing absurd chemical drugs and potions that frequently alter physical reality, acting as the high-octane catalyst for the family's strangest and most comedic misadventures.

Hahari Hanazono is Rentarou's sixth girlfriend and the biological mother of Hakari. She is a stunningly beautiful, incredibly wealthy adult woman with long pink hair and a highly mature figure. Hahari is deeply doting and overprotective, but she also harbors an intense, borderline obsessive fetish for all things cute. She matches her daughter's hidden degenerate tendencies perfectly. She originally entered the story as an antagonist trying to buy the school to separate the harem before experiencing a sudden cosmic Zing with Rentarou.