An OVA of SKET Dance bundled with the 29th volume of the manga, covering chapters 198, 199, and 200. This is a conclusion of some of the events shown in the last episode of the anime series.

Marin and her younger sister Urin are seafolk who happen upon something quite strange: a beautiful silver ring lost beneath the waves. The kind-hearted Marin, intent on returning it to its owner, drags a reluctant Urin along with her to the sky world despite reminders of a turtle elder who left for the surface and never returned. After locating the ring's owner, Kanon Miyamori, they learn that Kanon had tossed it into the sea after her boyfriend dumped her earlier that day. Though Marin insists that such a lovely item should not be thrown away, Kanon discards it once again. As they search for the ring, Urin becomes separated from the other two and accidently breaks the seal on a stone coffin, releasing an evil being known as Sedna. Sensing Sedna's release, the formerly missing turtle elder, Matsumoto, reveals himself to Kanon and her companions, naming Marin as the Priestess of the Sea. Together with the Priestess of the Sky, she has the power to seal Sedna away again. And as luck would have it, during an encounter with one of Sedna's minions, Kanon discovers that she is the Priestess of the Sky. Though Kanon is hesitant, she and Marin decide to work together to save the world from the evil that threatens it.

In post-WWII Japan, Prof. Shikishima has built up Shikishima Industries to be a technological powerhouse, working on developing robots. However, at the heart of their success lurks a dark secret from the war, something that cost the life of Prof. Kaneda, the mentor of Prof. Shikishima. Now Kaneda's son, Shoutarou, is about to learn the truth, and it will change him forever. (Source: ANN)

When Mitsuki learns that the highschool is going to destroy the old school building, she is saddened at the thought of so many memories being erased. Chitose and the rest of the moms spring into action to stop the demolition. During their efforts, Fumitsuki, Chitose, and Mitsuki finally realize their true feelings.