The Irregular at Magic High School, Vol. 11 (light novel) Visitor Arc, Part III.

At the same that the leader of the USNA's elite magician unit, the Stars, traveled to Japan under the identity of an exchange student named Lina, the parasite incident wreaked havoc on the First Magic High School until Tatsuya and his friends saved the day and brought the incident to a peaceful conclusion. However, the parasite merely lost its first host and continues to wander this world. More importantly, it's found its next host-a humanoid hel...