Daichi, Suga, and Asahi are #1, 2, and 3 on the team respectively – not just because they're the most senior members, but because contact in volleyball ideally goes receive —> set —> spike, which they specialize in respectively.
Before Karasuno's first practice match with Aoba Johsai, Kageyama wants to pick a fight with Hinata to calm him down. Why does he think it would work? Because he's seen how Hinata lost all traces of anxiety when Kageyama confronted him before their middle school match!
Nekoma's uniform is red with the libero's jersey having the colour white, symbolizing red blood cells and while blood cells respectively. Seems like Kuroo's Rousing Speech isn't something random, with the team's consistent playstyle being similar to red blood cells travelling to give oxygen (the ball) to the brain (Kenma). Similarly, liberos' defense also stands for while blood cells eliminate threats to the human body.
Ushijima claims that Aoba Johsai is infertile soil, which leads to the implication that Karasuno is concrete, and that Ushijima believes that they'll also never win. Except that plants which manage to grow through concrete have to be a lot tougher than plants which grow in perfect conditions in fertile soil, hence Karasuno beating Aoba Johsai and then Shiratorizawa, after overcoming their problems and blasting through their limits, like plants fighting for nutrients and then through concrete.
In Season 2, Episode 15, it's pointed out that Johzenji's banner, "Simplicity and Fortitude", is made ironic due to the unusual playstyle of Johzenji. However, looking at a few◊ screenshots◊, maybe it's not just the former generations of Johzenji it's talking about (Specifically, the In-Universe explanation given for the irony of the Johzenji banner is that it actually suited the team until recently). It's also referring to Daichi's playstyle; specifically, the fortitude his simple, defensive playstyle provides for the rest of the team.
In the final chapter Oikawa, who is one of the members representing Argentina at the 2020 Olympics, is stated by the announcers to have been an "Unknown Player" during his High School days. This is shocking at first until you remember that Aoba Johsai High never actually managed to make it to any of the National Tournaments during his time there due to the team always losing to Ushijima and Shiratorizawa Academy. Likewise, Oikawa was never recruited into the All-Japan team despite his talent.
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