Taiyaki are a traditional Japanese snack, often sold from impromptu stalls at festivals, but enjoyed at any time of the year. Tai means bream and yaki means baked. There was a famous pop song about Taiyaki many years ago.
They are made of a light batter with a filling. In Japan, the most common fillings are anko (sweet red beans), shiro anko (sweet white beans) or chocolate. If you are very tenacious in your searching, you can find many other interesting flavours, a quick look using a search engine resulted in 'Tomato sauce risotto' flavour, yum!
In some towns you can occasionally find Taiyaki or other Japanese cake stalls near the entrance to supermarkets or other shopping centres, such as below.
This is a stall I found in Nara. As you can see, you need a special hinged grill to make Taiyaki. You can also find a home Taiyaki maker, I'm definitely adding that to my wishlist.
During the course of my research, I found that other interesting flavours of Taiyaki are available outside of Japan.
In Chiang Mai, in the north of Thailand, I found Taiyaki being sold at the night market on Walking Street. They sold more flavours, such as cream, chocolate, blueberry, green apple, red bean (similar to anko), strawberry and Pandan custard.
I didn't know much about Pandan so I tried that one, it was similar to apricot jam. Pandanus is a kind of shrub, some varieties produce Pineapple-like fruits. It is not well known in the UK.
In Singapore I came across Ooki Taiyaki, they are located in the Raffles City Shopping Centre. They sell a variety of different flavours such as blueberry, kaya, pumpkin, peanut and durian. Being Singapore, the most popular flavour is durian. They also sell savoury varieties such as ham and cheese.