Episode 13 and 14 of Poputepipikku. The special has four versions shown on four different broadcasters: Tokyo MX (Blue Dragon ver.), Nico Nico Douga (Vermilion Bird ver.), Abema TV Anilive (White Tiger ver.) and Abema TV Pop Team Epic Channel (Black Tortoise ver.). Each version has a unique combination of seiyuus.
Source: MAL