You came for one more hit of the same nonsense, and that is exactly what this is: a thirteenth episode that only exists because someone bought the disc. The whole joke of Days of Urashimasakatasen was Urata reaching for that classroom door with a brilliant high school debut in mind and getting Shima, Sakata and Senra instead, and the show never let him recover from it. There is no arc here, no stakes, no thematic weight, just four guys running the same low-wattage bit at a runtime shorter than the time you spent picking something to watch. It works because the voices belong to the actual utaite the characters are drawn from, so the bickering has the worn-in rhythm of people who have genuinely been stuck with each other for years. If you already know which of the four you are, this is a bonus track, not a sequel. Play it and put the disc back on the shelf.

Urashimasakatasen no Nichijou gets one more episode in this OVA: a 13th installment that never aired and was released on the DVD instead. The original series follows transfer student Urata, who plans a brilliant high school debut to become the most popular student in class, only to find Shima, Sakata and Senra in his way. The show is a comedy with a slice-of-life feel.