Shoyo Hinata joins Karasuno High's volleyball club to be like his idol, a former Karasuno player known as the 'Little Giant'. But Hinata soon learns that he must team up with his middle school nemesis, Tobio Kageyama. Their clashing styles form a surprising weapon, but can their newfound teamwork defeat their rival Nekoma High in the highly anticipated 'Dumpster Battle', the long awaited ultimate showdown between two opposing underdog teams?
ONLY ONCE, ONLY 7TH. was the sixth live by the IDOLiSH7 franchise, held at the Yoyogi National Gymnasium. It was a celebration of the franchise's seventh anniversary and it marked a special milestone as the number "7" is very a significant number within IDOLiSH7. The theme was "parade".
The older boys are graduating school and recount their memories together. The next day everyone defends the graduation ceremony against Zundar and Dadacha's Second-Button Monster, but Yumoto struggles using his love power.
Karasuno High enters the Inter-High Volleyball Tournament and immediately proves they're "flightless crows" no more. After their first match, Karasuno dukes it out against Date Tech High and their famous Iron Wall, which shut down every spike of Karasuno's ace, Asahi, during a previous match. Later, Karasuno fights Aoba Johsai High and seeks to have the same outcome as their first practice match.
Shouyou Hinata, after losing to Kitagawa Daiichi Junior High's setter Tobio Kageyama in his first official volleyball match, transfers to Karasuno High, intent on finally having a proper volleyball team and getting his revenge on Kageyama. Upon arrival at Karasuno, however, Hinata finds out Kageyama has also gone to Karasuno. Initially at odds with each other, the two form an oddball combination and fight together with the other members of the volleyball club. Karasuno reunites with a former rival school, Nekoma High, in a practice match and reignites their school rivalry.