Unagi, or freshwater eel, is a very popular food in contemporary Japan and there is a dedicated ‘Eel Day’ in mid-summer (this year July 24th) on which most Japanese eat unagi
The simple explanation why is that this is the hottest time of the year and as unagi has lots of nutritional value and fat content, it gives you the umph to not wilt in the blazing, steamy summer heat.