Koyomi Stone is the first in a 12-episode miniseries of short stories involving Araragi Koyomi and all the other various characters in his orbit. First up is Hanekawa Tsubasa, whose dealings with Koyomi pre-date his girlfriend Senjougahara’s. Tsubasa presents him with a mystery of a stone in a shrine and asks him to report it to Oshino to see if it’s an oddity.
Oshino’s reply is for Koyomi and Tsubasa to study the high school’s curriculum. Tsubasa picks up on the clue and deduces the stone was once on its own until someone was about to toss their failed woodworking project into the nearby garbage, but placed the stone in it instead.
As a result, both objects changed: the stone became something that resembled an object of worship, and the failed house became a successful shrine. With the case closed, Koyomi remembers it was he who built the crappy house and put the stone in it; he later tosses the house and discovers the stone is really just a hunk of concrete.
The usual Monogatari style is all there to be seen and heard, adding weight to an otherwise slight and superfluous mystery, while the shorter runtime makes for easy watching.