Kaho Nikaido is the main protagonist of the story, a fifteen-year-old high school student who moves to Tokyo to live in a dormitory called the Kasumi Residence. Born on March 16, she is described as a cute girl with long dark purple hair that has a single strand sticking up, and purple eyes. She comes from an extremely wealthy family and is a late child of elderly parents, which resulted in a very sheltered upbringing. Because of her family's influence and status, everyone in her hometown treated her with excessive care and never criticized her, making it difficult for her to form genuine friendships as people were often interested only in her status or were paid to be her companions.

Despite her privileged background, Kaho is not boastful and makes an effort to live as normally as possible. Her personality is generally kind, caring, gentle, shy, sweet, and somewhat soft-spoken, though she is also noted to be naive and clumsy. Having never been scolded or spoken to harshly, she is initially taken aback when a tall young man named Kanade Takahashi saves her from being hit by a truck and angrily tells her off for her carelessness; this direct and honest treatment, which she had never experienced before, is what sparks her attraction to him. Upon meeting him again at her new dormitory, she boldly confesses her love, believing it to be destiny, only to discover that her new boyfriend is actually a fifth-grade elementary school student, making him five years younger than her.

This central, problematic situation defines her role in the story. Kaho is fully aware of how inappropriate it is for a high schooler to have feelings for an elementary school student, and she is constantly self-conscious and worried about the relationship. She often wonders if she should continue dating Kanade, but she is also prone to fits of jealousy and possessiveness when she sees girls his own age interacting with him. Throughout the series, she tries to navigate a romance where her boyfriend's physical appearance, which is that of a tall, handsome older boy, is in constant contrast with his childish behavior and emotional development. As she has never had a real relationship or even experienced unscripted play as a child, dating Kanade inadvertently allows her to learn about natural social experiences she missed while growing up in her protected environment.

Key relationships in her life include her boyfriend, Kanade Takahashi, who despite his age is the object of her first love; and her older brother, Daikoku Nikaido, who has a morbid and obsessive doting nature towards her. At the Kasumi Residence, she lives alongside other tenants such as Chiaki Yokoichi, who serves as a voice of reason, and Kouta Shinohara, a shy first-year high school student who has a crush on her. She also deals with Atsushi Taga, a college student who initially acts as her rival and displays a hostile attitude toward her.

In terms of development, Kaho begins as a very sheltered and insecure girl with low self-esteem due to the artificial nature of her past relationships. Her journey involves confronting the absurdity of her situation. While she often reacts with shock or confusion to the chaos around her, she also experiences significant moments of clarity. Notably, she has a more serious side that emerges, where she takes even small things to heart and speaks her mind without reservation. By the conclusion of the anime, she reaches a breaking point and explodes, calling out all the ridiculous twists and excuses she has had to put up with, revealing that underneath her naive exterior, she is completely aware of how senseless the situation has been. A notable, albeit uncomfortable, running gag involves her being seen in her undergarments by Kanade and his friends.