When Haruhi Suzumiya's emotions become unbalanced, closed space is created in a limited area as a way for her to release her anger and frustration through creatures called celestials. It is the duty of an 'Agency' esper to remove the celestials, which destroys the space. Closed space is characterized by gray skies and loneliness. Esper Itsuki Koizumi pointed out that Haruhi's depression does not cause closed space, only frustration. He asked Kyon to avoid doing anything which would trigger Haruhi to create closed space (in other words, keep her happy and entertained).