The Irregular at Magic High School – Ichijou Masaki’s Diary Arc

A terrorist bombing strikes the Ten Master Clans Conference. In order to investigate the incident, Ichijou Masaki, the eldest son of the Ichijou family, one of the Ten Master Clans, known as the Crimson Prince, temporarily transfers from Third High School to First High School. This also means becoming classmates with the goddess he admires, Shiba Miyuki.

A spin off from the main story of Mahouka Koukou no Rettousei Shizoku Kaigi-hen

The arc follows volume 19 of the light novel.