Masaki is the second son of the Ward family, a household renowned for its legendary survival skills and many experiences involving cats. Within his family, he is regarded as the smart one, known for balancing wit and empathy, a combination that earns him respect from his siblings and peers. He works alongside his father, Kouji, and his older brother, Len, gathering supplies in a world transformed by a virus that turns people into cats upon physical contact. Early in the story, Masaki and Len go missing after a supply run to a mall, where they become completely overwhelmed by cats. Their father sacrifices himself to buy them time to escape, becoming infected in the process. Masaki and Len are forced to take shelter in a storage room, surviving on snacks until they are found by a trio of survivors led by a green-furred Devon Rex cat. They then join this group to continue gathering supplies and look for a way to escape the feline-infested wasteland.

Masaki has long, dark hair that covers one of his eyes, and his eyes are blue. He typically wears a black coat and pants with a green shirt, and his signature weapon is a pair of blue dolphin-shaped pistols. He is a capable fighter who understands the risks of the Nyandemic and follows strict protocols to avoid infection. Stoic and reliable, he serves as a pillar of strength for the research team. His primary relationship is with his brother Len, with whom he shares a deep professional and personal bond. He also coordinates with Kaoru on tactical defense strategies for their research outposts. Masaki is often the one to implement the practical applications of Len's findings, such as testing new deterrents against the feline hordes. His development is closely tied to the success of their research, facing increasing pressure as the cats become more aggressive, forcing him to adapt his combat style to protect the group's last hope for a cure. Throughout the story, he remains a steadfast survivor driven by the need to protect his family and contribute to humanity's survival.