What even is a Harvest Show?
The official site (Japanese) describes it as

Harvest Show
It is a live performance for the grains to appeal for their deliciousness to the surroundings.

which is basically the same as what MAL and ANN describes

[...] to perform at the &quot;Harvest Show&quot; to show the delicious appeal of rice grains.

How or what do they do, don't ask me... but in addition to its comedy genre, the show is full of parodies.

Sasashiniki stopping a bullet train from hitting a dog in episode 5 is actually a parody of Kinnikuman about Terryman stopping a bullet train... from hitting a puppy. Wikia stated,

In the 21st Olympics, he (Terryman) made it to the third preliminary round, shoving bullet trains, but was disqualified for stopping his train from hitting a puppy (touching the train twice resulted in a disqualification)

Image source

Reference: ほかこ's Hatena Blog (Japanese)

The cross-dressing idol unit in episode 3 is certainly a parody of many idol units (as seen in the naming proposal): iM@S (maiM@S), PriPara's SoLaMi♡SMILE (KoMeMi☆SMILE), Aikatsu! (MaiKatsu), Love Live! (Love Rice), etc.