personally, i think that the parallels between the pied piper and goethe/faust are intentional! the themes that wataru speaks about runs true through either...

but the storyline in the story is explained to be the one from the poem, of the pied piper drawing the rats away, drowning them in the river, then upon not being paid, draws away the town's children. it is worth noting it is yuzuru that gives the story summary, but wataru affirms it and agrees that a story about children being lured away isn't suitable for a family amusement park. he later clarifies to eichi that he was hoping that perhaps it could be approached from a different angle, one that gives it a happy ending.