Hiiragi-iwashi is a holly sprig with a baked sardine's head, and Japanese people have a time-honored custom of putting Hiiragi-iwashi at their door on Setsubun (the traditional end of winter) to ward off evil spirits. It is also called Yaikagashi (burn and smell), Yakkagashi, Yaikusashi or Yakisashi.
They say that prickles of holly leaves prevent Oni (ogre) from entering through the door by piercing Oni's eyes, and that the smell of sardine chases Oni away (on the contrary, another explanation is that the smell of sardine invites Oni to approach and then prickles of holly leaves pierce Oni's eyes).
According to Tosa Nikki (Tosa Diary), in the Heian period, a holly spring and a head of 'Nayoshi' (striped mullet) were on Shimenawa (sacred rice-straw rope) which was displayed above the door on New Year's Holidays. Even today Shimenawa with a holly sprig is sold at Ise-jingu Shrine on New Year's Holidays. It seems that this custom was also widespread in the Edo period, because it can be seen in Ukiyoe (Japanese woodblock print) and Kibyoshi (illustrated book of popular fiction whose cover is yellow). In Nara City, Nara Prefecture many families still follow this tradition and Hiiragi-iwashi is quite a common sight, but in Kyoto City, Kyoto Prefecture you seldom see Hiiragi-iwashi. This custom is not widespread any longer but can be still seen throughout the Kanto region and in Fukushima Prefecture. In the area near Tokyo, Mamegara (a soybean sprig after removing seeds) is added to holly and a sardine's head.