Masaru Kondo, an 11-year-old central character, stands five feet tall with black spiky hair and brown eyes. He typically wears a yellow shirt featuring orange horizontal stripes, blue jeans, and white-and-red shoes. Known as kind-hearted and generally popular among classmates, Masaru also possesses a competitive streak, sometimes showing off new possessions to provoke envy in peers like Obochamma Kun. This tendency surfaces in rivalries, particularly with Asato.

Though usually warm and polite, disruptive behavior from his best friend Hagemaru can trigger Masaru's temper, leading to reciprocal pranks or retaliations. Despite these moments, he maintains fundamentally amicable relationships with Hagemaru and his wider social circle. Masaru consistently shows kindness to female classmates and close friends, expressing a noted romantic interest in Nikori Yamada, identified as his girlfriend. He shares a friendship with Obochamma Kun and cares for pets, including several turtles named Maddy, Rex, Lucifer, Simon, and Elvis.

His family includes parents Mr. and Mrs. Kondo. Masaru's mother appears sweet-natured and polite but occasionally engages in rivalrous behavior with Hagemaru's mother, Aiko Hageda, especially in displays of one-upmanship, subtly mirroring Masaru's own showing-off tendencies. His father is described as caring, handsome, and tall, contrasting with Yuji Hageda. Family interactions suggest a supportive household, with Masaru occasionally accompanying his parents on outings, such as visits to a village.