"Kaisu-Wari? Yes, It seems to be interesting."
...This is a product of usual activity in pixiv. In summer, there was an event on the theme of summer, and I painted this. Tsukuyomi wearing summer clothes!
The subject of this is a Japanese play called Suika-Wari(スイカ割り, The game that blindfolded person chops a watermelon with the helps of the voices of persons around him or her).
Since he cannot swim skillfully, he solely plays Suika-Wari at the beach.
However, this is the Pokemon world, the fruit he chops is not a watermelon but a Watmel Berry W.
(※ Watmel Berry called Kaisu in Japan. By the way, watermelon called Suika.)
It is the wooden sword of Tachi(太刀, long sword) which he has. (Niten-Ichiryuu specifications)
He seems to be mistaking the event for another event W.