There are 25 of these previews (since there are 26 episodes, and episode 1 doesn't get one, naturally). BD volumes 1-12 come with two each; volume 13 comes with one. Each preview is 30 seconds long, and perhaps reflects what KyoAni had planned to use as the previews before switching to the scheme they actually used (non-sequitur voiceovers from guest voice actors, mostly).
Video-wise, all of them are set to footage that was already in the main series; the only new part is the audio. What follows are brief summaries of the contents of each one, starting with the preview for episode 2. Note that the previews for episodes 6 and 7 are missing because I haven't actually seen those.
- Yukko/Mio. Yukko and Mio talk aimlessly about zodiac signs. Yukko reports the death of one "Mikhail Libra", age 55.
- Nano/Sakamoto. Nano calls Sakamoto various things ("Sakamoto-kun", "Ryouma", etc), and Sakamoto gets generally offended by said things.
- Yukko/Mio/Mai. Mostly Yukko making hilarious sound effects ("Za! Guwa! Shu! Zubaan! Strike!", etc).
- Yukko/Mio. Picks back up with zodiac signs after the episode 2 preview. "Let's combine Cancer and Scorpio into 'Crustacean!'", suggests Yukko.
- ???
- ???
- Dolph / Princess Starla. Dolph says things in a funny voice.
- Nano/Hakase. Hakase makes Nano capable of getting cavities. Nano enjoys this (it makes her more normal), but then she notices that something hurts. Turns out that Hakase also just gave her a cavity right off the bat.
- Yukko/Mai/Mio. Yukko writes "E" on the back of her hand, but can't remember what she meant by it. Mai and Mio try to guess, but fail. Turns out, it was "European heart urchin", which is apparently a meme.
- Yukko/Mai. Yukko asks Mai what a "Living National Treasure" is. Mai tells her that to become one, you must be able to recite the contents of a large number of textbooks by heart. This is, of course, a joke.
- The vice principal / the principal. The vice principal tells the principal to say words like "pappelbon" and "shishikabago". The vice principal is rather amused when he does so, unnerving the principal.
- Annaka / Ms. Sakurai. Annaka starts calling Ms. Sakurai "Ms. Izumi", which makes her very nervous.
- Hakase/Nano/Sakamoto. "Is 'borscht' food?" Yes. "Is 'shark chocolate' food?" Yes. "Is 'shark' food?" Yes. "Eeeeeek!"
- Yukko/Mio. More zodiac signs. Yukko is troubled by Gemini being two people yet only counting as one zodiac signs. Why not split them up into separate Castor and Pollux zodiac signs?
- Mr. Takasaki. He teaches his students about the power and versatility of the (English, not translated) word "ENOUGH!". And also "baka".
- Yukko/Mio. Yukko gets "San Francisco" and "Francisco Xavier" mixed up.
- Makoto / Mr. Takasaki. Makoto asks Mr. Takasaki to be the advisor for the go-soccer club, and offers to set him up with his sister in exchange. Naturally, Mr. Takasaki is hugely flustered.
- Misato/Mihoshi. Misato is feeling down; Mihoshi suggests she ask Sasahara for help. Misato then blows something up. Classic gundere!
- Hakase/Sakamoto/Nano. Hakase pretends to be a maid and serves Sakamoto food - but using a mortar and pestle, which Sakamoto is affronted by.
- Yukko/Mai. Yukko says "selamat pagi" to Mai; they then have a conversation in what I assume is Indonesian. Yukko eventually gets frustrated and says "bakayarosu" (sounds like baka yarou "you fool"), which Mai points out is a food. This appears to be a Japanization of the Greek word for "cod" (μπακαλιάρος / bakaliáros)? Nichijou is weird sometimes.
- Nano / Ms. Nakamura. Nano comments on the cuteness of Ms. Nakamura's streetwear; she is thrown quite off guard by this.
- Yukko/Mio. Yukko's still going on about zodiac signs; this time, it's Ophiuchus. Seriously, what's the deal? You can't just add another zodiac sign! What is he, a transfer student? "Your seat is the one between Scorpio and Sagittarius"? And then Virgo falls in love with him, and Aquarius gets jealous of them, and suddenly! Mikhail Libra out of nowhere!
- Hakase/Mai. Hakase asks Mai what she's drawing; in typical Mai fashion, she's drawing Gōzanze Myōō, "space", and something else I don't quite get. "Are there sharks in space?" asks Hakase. Apparently, yes.
- Mihoshi/Misato. Misato vigorously denies ever talking to Sasahara or even being acquainted with him at all. She closes with "it's not like the next episode is going to be episode 25 or anything, okay?".
- Nano/Yukko. Nano tries to ask about how Yukko often calls herself an idiot. Yukko replies that "she's an idiot, but also a genius, so it's okay".
