The biggest summer festival, "Otaru Ushio Matsuri" will be held on Jul 29th ~ 31st.
We're arousing this festival already in same "Ushio Matsuri" T-shirts.
The mark on our backs is the symbol of "Ushio Matsuri".
It represents wave.
"潮" is read as "Ushio" and means tide.
Cool, isn't it?