1. Build the fishing cabin. To do this, use 200 lumber, 20 silver ore, and 2 copper ore then talk to Takakura (the carpenter) with all the materials.
2. Befriend the turtles near the waterfall area. You can give them rice cakes or grapes to gain friendship points. If you're married to a girl in the game, they'll bring home an egg that will then hatch into a pet turtle.
3. If you've befriended the turtle by winter and are not married in the game, Takakura will bring you a turtle on Christmas Eve.