Japanese traditional sweets, known as wagashi, have long been associated with good fortune and gift giving, and Traditional Sweets Day has been observed for more than a thousand years. Today, wagashi are still an important part of the Japanese tea ceremony, and the hundreds of varieties of confections are also a popular treat.
For example, dorayaki, a sort of pancake filled with sweet red bean paste, is still very much a popular snack.
— Yuuki (@ore_english) June 15, 2017 
To kick the day off, a Japanese yuru-kyara or mascot holding a dango, a popular traditional sweet, explained the origins of the day:
— たいしくん (@taishi_cho) June 15, 2017 
Hi, I'm Taishikun, Osaka's official wagashi ambassador. On June 16 it's wagashi no hi! Long ago, in the olden days, on the 16th we would eat 16 pieces of wagashi to ensure happiness. The day was originally call “kajou” (嘉祥, 嘉定). And so the 16th is wagashi no hi.
Yet another mascot, Gunma-chan, who represents the Japanese prefecture of Gunma, showed off some elaborate wagashi that are representative of the delicate details common in some varieties of Japanese sweets:
— ぐんまちゃん投票応援アカウント (@gunmachan_toa) June 16, 2017 
[…] Since today is wagashi no hi, here are some wagashi that look just like me, Gunma-chan. These were made in the city of Kiryu, in the mountains of Gunma.
Many people are uploading photos of their own favorite traditional treats:
— さゆき (@_sayuki_12) June 17, 2016 
It seems like today is wagashi no hi! Here's a photo of some momoyama (a confection made with rice flour) and nerikiri (a sweet made from white azuki bean paste, sugar and yamaimo, a kind of starchy mountain yam) that I ate a while ago.
— みずっち@羅夢 (@hibi_miz) June 16, 2017 
[…] Here are some photos of my favorite Japanese traditional sweets. (❁´ω`❁)
Wagashi come in all shapes and sizes, some whimsical and others more like works of art.
— ＭＡＭI (@sakura4200) June 17, 2016 
These are super tasty #awesome_photos #photo #wagashinohi #follow_me
Just as wagashi are connected to traditional Japanese culture, so is the old imperial capital of Kyoto, which has its own traditions associated with the tea ceremony and sweet confections. One Japanese cafe has capitalized on wagashi no hi to invite people to try out its own beautiful creations in the lead up to the Gion Matsuri , one of the most famous festivals in Japan that is as old as the thousand-plus year-old tradition of wagashi no hi itself.
— 玉露cafe 喫茶去京極 (@gyokurocafe2008) June 16, 2017 
Good morning! It's just a couple of weeks until the Gion Matsuri and the beginning of summer in Kyoto. […] Kyoguku , our traditional Japanese cafe, will be open today for wagashi no hi starting at 11:30AM. We hope to see you!
#Shimizu Temple #Japanesestylecafe #wagashinohi
Japanese wagashi are not just limited to delicate confections. Shaved ice, served with macha tea and a macha syrup, is also popular in some traditional Japanese cafes.
— 香川愛生@17日JCGｼｬﾄﾞｳﾊﾞ-ｽ (@MNO_shogi) June 16, 2017 
It's wagashi no hi, so we're having macha.
Of course, marketers are also trying to take advantage of the hashtag on June 16. Giant candy maker Glico reminded everyone about their own product. While not exactly a traditional, this Japanese snack has become popular all over the world.
— pockypretz11 (@pockypretz11) June 16, 2017 
It's been more than 50 years since this candy was first introduced to Japan. #wagashinohi
To see more photos of traditional Japanese sweets, follow the hashtag #和菓子の日  on Twitter.