Shōyō Hinata was inspired to play volleyball after seeing Kurasuno High School's "little giant" competing in the national tournament on TV. He trains relentlessly to make up for his lack of height, but suffers a crushing defeat in his first and last tournament of middle school at the hands of his rival Tobio Kageyama. Vowing revenge against Kageyama and hoping to follow in the little giant's footsteps, Hinata joins Kurasuno High School's volleyball team. To his initial dismay, Kageyama is also on Kurasuno's team. The former rivals soon overcome their differences though and combine their strengths to form a legendary combo using Hinata's mobility and Kageyama's precision ball-handling. Together with their team, they compete in prefecture tournaments and promise to meet Kurasuno's fated rival school at nationals.
In preparation for Spring Nationals, the boys' measurements are taken, invoking friendly competition amongst the team. Kageyama is invited to the All-Japan Youth Training Camp, while Tsukishima is invited to the first-year only prefecture-wide training camp. In a fit of jealousy, Hinata sneaks into Tsukishima's camp. Despite the initial confusion, Shiratorizawa's coach allows Hinata to attend the camp as a ball boy to test his skills independent of Kageyama.
Hinata was lectured after causing trouble by Sawamura Daichi, Coach Ukai and his school Teacher Advisor's Takeda, who said "He who climbs the ladder must begin at the bottom". Back at Shiratorizawa, Hinata observes the practice session as a ball boy. A surprise match against Shiratorizawa's third years and alumni was set up for the camp participants. In between sets, Hinata took a moment alone in the equipment room.
With Coach Ukai's advice in mind to not go underestimating what it takes to be a ball boy, Hinata comes out with a clearer mind. Hinata works on receiving the ball in different ways by reading the spikers' form, a skill that he learned in middle school. For personal training, Hinata volunteers to be on the receiving side in an effort to practice his split form. Back at Karasuno High, the boys had a practice match with Tokonami High while they practicing on their serves, realizing that they preferred to do the penalty whether they win or lose. Kageyama continues his practice at National Youth Camp and subconsciously set his toss higher than usual.
Tsukishima surprised Hinata by joining the Blocking Practice session. At the National Youth Camp, Kageyama had been the most reserved attendee. Sakusa is curious about the Karasuno-Shiratorizawa qualifying match. Later, he was challenged by another setter, Miya Atsumu. Back in Shiratorizawa, Tsukishima realised that he isn't the tallest in the group. He tries to find various tactics to block future spikers in the upcoming national tournament. As a ball boy, Hinata has been observing Kunimi's characteristics. Being the newest and the tallest attendee, Hyakuzawa from Kadokawa High couldn't keep up with the training. Hinata is able to encourage him by telling him to take things easy which helps Hyakuzawa on track with his training.
As a ball boy, Hinata has been observing each player, mirroring their playing styles and asking numerous questions about volleyball. In Tokyo, Kageyama has been exposed to various positions aside from being a setter and has made acquaintances who he will see at nationals. Back at Karasuno, the boys have been practicing on their serves. Takeda has been contacting various schools for practice matches before the Spring tournament. The next morning, Kageyama and Hinata reunite. Kageyama is pleasantly surprised that Hinata has been a ball boy at the camp and they both share information about the attendees. The team finds out that Date Tech will be the first school on the list for Karasuno.
On their first day back, the boys practiced on their serves. Kinoshita is able to float serve while Yamaguchi has yet to master a jump serve. Hinata surprised everyone by being able to receive Kageyama's powerful serve. For personal training, Kageyama coaches Hinata on his jump technique by using Hoshiumi as his reference. Date Tech comes over to Karasuno for a friendly match. The boys face various new challenges from Date Tech's newly evolved "Iron Wall" defense.
Kageyama have been on the edge since his return from Tokyo. He refrained his old habits by being silence. Hinata managed to ease the tension by reminding Kageyama of his growth since they met. Coach Ukai used this opportunity to encourage the team to have effective communication. Later, Kageyama experimented his tosses with Tsukishima to break through the "Iron Wall".
The practice match against Date Tech is now into the fourth set. Coach Ukai decides on Kinoshita after seeing him hiding and avoiding eye contact. Coach Ukai encourages Kinoshita by acknowledging his ability to score but warns him not to pull the vanishing act again. Karasuno continues to employ their newly learned techniques and finds them effective even against the iron wall. Ultimately, Asahi breaks through three blockers to clinch the final set, resulting in both teams having 4 wins and 4 losses.
It's New Years Day. Daichi is on edge due to the incoming Spring Inter-high, but a day of spending time with his teammates and friends helps him calm down. The team has arrived in Tokyo for nationals. After getting some practice in at a local gymnasium, the team settles down at their lodging, where each member spends the last night ahead of the big day in his or her own ways. The day after, Karasuno reunites with Nekoma, Fukurōdani, and some other familiar faces at nationals.
After the opening ceremony, the team goes to warm up for their first match at another gymnasium. When they return to the official venue, Hinata discovers that he has grabbed the wrong bag and is missing his shoes. Kiyoko goes to retrieve Hinata's lost bag while the team warms up for their first match. As she ran to the station, she recalls her memories of when she first became the manager and her journey with the volleyball team. Kiyoko returns to the gym just in time with Hinata's bag that contains his shoes ahead of Karasuno's match against Tsubakihara Academy. Just like Coach Ukai expected, the process is much tougher than expected. Kageyama is having a hard time adjusting to his surroundings which is affecting Karasuno's first match against Tsubakihara Academy. The only thing his teammates can do is hold out until Kageyama recalibrates. Yamaguchi is switched in with Hinata as a pinch server and manages to change the momentum for Karasuno. Finally after trial and error, Kageyama and Hinata manage to successfully pull off their quick. The score is currently 13-15 with Tsubakihara in the lead.
Former Karasuno members appear to cheer on the new team and are impressed by the growth of their old teammates as well as the abilites of the first years. Kageyama, in particular, is attracting a great deal of attention for his superior technique and sharp game sense. Meanwhile, Atsumu Miya observes the match and finds Kageyama a completely different player. He also takes an interest in Hinata. Tsubakihara persevere and enters into a long rally with neither team willing to give up. Just when Tsubakihara seems to have broken through Karasuno's defenses, Hinata manages to keep the ball in play by receiving it with his chest, and Asahi follows up with a spike to even the score 18-18. Hinata is still having trouble finding the right position to receive, but his improvements are becoming noticeable to his teammates. Moreover, it's not just Hinata, the whole team has grown immensely. Tsubakihara's Himekawa is switched in as a pinch server at a crucial moment for Tsubakihara. Under pressure, Himekawa accidentally serves the ball into Teradomari's head. This gives Karasuno the last point needed to win the set. The second set begins and eventually ends with Karasuno in the lead 15-14. Himekawa is switched in once again, but this time he successfully pulls off a ceiling serve, which sends the ball high into the ceiling by using a underhand serve. Daichi completely misses the ball because of the gymnasium lights, allowing Tsubakihara to regain some momentum. Karasuno initially struggles with the serve, but they soon adapt and halt Tsubakihara's momentum. Karasuno refuses to be left behind as they gradually make their comeback. The game continues in a intense rally with both teams scoring back and forth. With the score at 23-23, Karasuno makes a miscoordination but Daichi saves it just in time to put his team at match point. For the last play, Sugawara joins the match as the pinch server, aiming to cause a disarray in their opponents formation. Both teams are refusing to give in, keeping up a good rally. Maruyama spikes the ball and it ricochets off the blockers but Sugawara covers it. The match ends with a finishing blow from Karasuno's ace, Asahi! Karasuno moves on to the second round!
Karasuno has won their first match at nationals and will be moving on to the second round. Everyone celebrates and the two teams bow to each other and to the audience. Daichi also realized that the former Karasuno members were there to cheer them on the whole entire time. The third years get to catch up with their upperclassmen who are amazed by Karasuno's current first years. While Karasuno is eating lunch, they decide to watch Nekoma's first match. Nekoma wins their first match at nationals as well and will be moving on to the second round. Meanwhile on Court E, Fukurōdani is just starting their first match against Eiwa and Bokuto is already in "dejected mode". However, the team is well-adapted and knows what to do while waiting for Bokuto to get over his slump. Once Bokuto regain his composure, he leads Fukurōdani to an overwhelming victory over Eiwa. Hinata, together with Yamaguchi, runs into Hoshiumi and immediately enters into a staring competition. Kageyama appears to introduce him as Kourai Hoshiumi, a member of the National Training Youth Camp. Hoshiumi questions Hinata about his position, height, and highest reaching point. Eventually Hoshiumi's teammate comes to get him, and the leave to get ready for their match. Karasuno members watch Hoshiumi's team, Kamomedai, and are amazed by his skill. Hoshiumi shows off his all-rounder prowess, leading the game commentators to call him the "Small Giant". Hinata is inspired by Hoshiumi's play and is glad they made it to nationals. It is the end of the first day of the Spring Interhigh. Before Karasuno heads back to their lodging, they encounter their fated rival Nekoma. They greet each other with Daichi and Kuroo reminding the other to survive the next day before heading their own ways. Karasuno gets some much needed rest after an intense day before the team starts preparing for their next opponent. Meanwhile, Tanaka finally gets the chance to talk with his childhood friend, Kanoka Amanai.
The night before the second day of nationals, Karasuno prepares to play against their next opponent. It turns out they are facing the runner-up of the Interhigh Tournament, Inarizaki High. Coach Ukai briefs the team about the players to look out for, especially Atsumu Miya who attended the Youth Training Camp with Kageyama. Karasuno quick realizes they are in for an incredibly tough match, but things get worse when they found out that Atsumu Miya has a twin.