Ayaushi shiryu! Cloth no hakaba - S1-E10
Stupidity: Saori blushes when Seiya opens the door shirtless...but she's seen him shirtless practically all her life, the boys kept training and fighting all the time. He even fought shirtless for the last part of his duel with Shyriu just the day before.
Stupidity: Amazing how people on this show, like The Accused here and in the earlier episode "The Chef", are leaving their doors unlocked or no explanations given as to how the actual killer planted the evidence.