Description
Kotori Toyomi studies at Millennium Science School as a member of its Engineering Department. Renowned for her extensive knowledge and talkative nature, she frequently delivers exhaustive explanations on mechanical concepts and historical contexts. This habit earned her the nickname "Walking Encyclopedia." When mechanical problems occur at Millennium, Kotori often arrives first to meticulously analyze and explain the situation. Others sometimes avoid her to prevent lengthy lectures. Discussing personal topics like hobbies or preferences makes her hesitant and flustered.

Her appearance features bright orange, messy bob-cut hair with bangs and a small left-side braid. She wears black glasses and has bright red eyes. Kotori's standard attire is a navy blue winter coat over a white shirt, a loose blue tie, an unbuttoned pleated black skirt, white socks, and black sneakers with blue laces. She carries a white Dillon Aero M134 "Minigun" machine gun nicknamed "Professor K" or "EX-Plain." Her halo displays an orange triangle inside a larger triangle with three angled arrows and hexagonal shapes.

In the "Beautiful Day Dreamer" narrative, Kotori appears after Momoi is struck in the head by a ball from the Engineering Department. She explains Momoi's unconsciousness and reveals the subsequent adventure—a baseball match, rescue mission against Wakamo, and confrontation with Binah—was entirely a dream. This revelation helps Momoi recognize the dream provided inspiration for the Game Development Department's video game project.

Kotori participates in Millennium events like a sports day, where she wears an orange-and-white cheerleader top, a navy blue mini-skirt, leg warmers, and carries pom-poms. She uses a modified version of her machine gun during this event, continuing her explanatory commentary while cheering. When the Engineering Department's plan to deploy a "cheerbot" fails, Kotori and others become cheerleaders themselves. She appears comfortable in this unexpected role. Her technical expertise includes modifying equipment, such as adapting her machine gun for the sports day. Kotori remains a consistent Engineering Department figure, applying her mechanical knowledge across diverse scenarios while maintaining her characteristic explanatory style.