Prepare the rhubarb swirl: In a small saucepan, combine the diced rhubarb, 1/4 cup sugar, and water. Heat over medium heat, stirring occasionally, until the rhubarb softens and breaks down into a thick sauce (about 8-10 minutes). Remove from heat and let cool completely.

Prepare the crust: Line an 8x8 inch baking pan with parchment paper, leaving an overhang on two sides for easy removal. In a medium bowl, mix the graham cracker crumbs and 1/4 cup sugar. Pour in the melted butter and mix until the crumbs are evenly moistened. Press the mixture firmly and evenly into the bottom of the prepared pan.

Make the filling: In a large bowl, beat the softened cream cheese until completely smooth. Gradually beat in the powdered sugar and vanilla extract until combined. In a separate, clean bowl, whip the cold heavy cream until stiff peaks form.

Combine and layer: Gently fold the whipped cream into the cream cheese mixture until just combined. Spread half of the cheesecake mixture over the crust. Dollop spoonfuls of the cooled rhubarb sauce over the filling. Use a knife or skewer to gently swirl the rhubarb into the cheesecake layer. Top with the remaining cheesecake filling and gently swirl one last time.

Chill and Serve: Cover the pan loosely with plastic wrap and refrigerate for at least 6 hours, or preferably overnight, until the cheesecake is firm enough to slice. Use the parchment overhang to lift the entire block out before cutting into 12 squares.