Itsuki Koizumi is an exchange student at est. jr. high, he too was forced to join the sos Brigade by Haruhi Suzumiya only he came more willingly than the others. Koizumi is an esper and he works for a company called the corporation, he fails to say what the corporation is but he does spill its purpose, to prevent Haruhi from getting bored.

Koizumi enjoys every activity the SOS brigade (meaning Haruhi) wants to do even though he very rarely comes up with any ideas.