If there’s grass on the ground and fins in your hand, you need to raise that hand up to the sky. You’re in the middle of a fisherman’s ritual, which can only be performed on grassy ground. You take fish fins from the previous year, and raise them up to the sky in order to ensure a good fishing harvest.
This ritual only works in one part of the world however. It absolutely must be performed in Little Kyoto (きょ). The way Little Kyoto lines up with the sun and the sky and all that astrological junk makes it the best place for you to raise fish fins up in the air.