Itsuki Koizumi is a fictional character from the anime and light novel series The Melancholy of Haruhi Suzumiya, created by Nagaru Tanigawa. He is a member of the SOS Brigade, a club formed by the protagonist, Haruhi Suzumiya. Itsuki is known for his calm demeanor, intelligence, and mysterious background, as he is actually an esper with special abilities. In the series, Itsuki often assists the main characters in navigating various supernatural events. He has a close relationship with Kyon, the series' narrator, and frequently provides insights into the strange occurrences surrounding Haruhi. His character adds depth to the story, blending elements of science fiction and mystery.