Mayuki Ikari first approaches Yūji Yagami by leaving handmade Valentine's chocolates, deliberately writing her given name ambiguously as "Masayuki" – a male name. This sparks confusion and leads to Yūji being teased when the gift seems to come from a boy. She resolves the misunderstanding by personally meeting Yūji after school at the front gate, revealing her true identity and starting their routine of walking home together.

Her personality blends shyness and indecisiveness, taking considerable time to confess her feelings to Yūji. This initial hesitance contrasts sharply with her notable temper; she frequently expresses frustration at Yūji's own indecisiveness and emotional conflicts. She owns and operates a bullet bike, embodying her assertiveness and independence.

As their relationship deepens, Mayuki becomes Yūji's girlfriend. Their interactions form a central narrative thread focused on navigating typical adolescent romance challenges. Her presence and influence directly aid Yūji in untangling his complicated feelings toward his mother, marking his shift toward conventional romantic attachments. The story chronicles their growing bond, tracing the evolution from tentative meetings to a committed partnership.