Following up last weekend's reveal, Famitsu's website has recently updated the bigger picture of this collaboration frame on the Taiko side. Together with the (still unknown) P&D X songs coming to Dokodon! Mystery Dungeon, Walking Through The Towers will make a rampant return as free DLC.
All the collaboration content will be available for free from the P&D X games' release (July 28th) to the end of August, after which month the content will be converted as paid DLC.
Source: [Famitsu.com]