S1·E97 Ghost Story! Old Man Willow!

Onsen-Mark tells the class a story of a cursed willow tree, which Ataru finds a load of fluff and ends up releasing an old man after Mendou after he carved his company's symbol with a knife on said tree. The old man drops a map to a possible treasure, while Mendou plans to see him at midnight to settle a score regarding the mockery of his company logo Ataru carved on the back of his robe. Meanwhile, Onsen-Mark is forced to do guard duty across the school by himself at night.