Mishiru, a butterfly-like Cocotama, emerged from the Yotsuba family's mailbox, earning her designation as "The Post God." Her full ceremonial name, "Miru Miru no Shiru Shiru no Scoop get-no-Mikoto," signifies her connection to observation and information gathering. Visually, she features red and tan coloration, large green eyes, pink cheeks, and rounded pigtail-like ears framing her face. Her distinctive tail bears white stripes, while the symbol on her eggshell underpants is a green envelope, reflecting her postal origins. For covert spy missions, she adopts a disguise with yellow and purple butterfly-shaped sunglasses and lipstick, operating under the codename "346."

Personality-wise, Mishiru blends shyness and childishness with stubborn and mysterious traits. She exhibits manipulative tendencies, frequently sneaking around Kokoro's room to gather intelligence on other Cocotamas, aiming to discover weaknesses that could secure her position as queen of the Cocotama House. Her spoiled side surfaces when she cries if her desires are unmet or her schemes exposed. She holds a particular dislike for bell peppers.

Mishiru's character undergoes significant development. Initially antagonistic, her persistent attempts to infiltrate and dominate the Cocotama House eventually give way to a change of heart. Following repeated failures and confrontations about her actions, she experiences redemption, expressing a sincere desire to abandon her manipulative ways. This leads her to choose cooperative living alongside Luckytama and the other Cocotamas within their community, transitioning from adversary to ally.